A(n ∞-)category with $G$-action is just a functor $BG\to \mathrm{Cat}_∞$. Then, if $\mathcal{C},\mathcal{D}$ are (∞-)categories with $G$-action, we can get another (∞-)category with $G$ action $\mathrm{Fun}(\mathcal{C},\mathcal{D})$ by pairing them: $$\mathrm{Fun}(\mathcal{C},\mathcal{D}):BG\xrightarrow{(1,i)}BG^{op}\times BG\to \mathrm{Cat}_∞^{op}\times\mathrm{Cat}_∞\xrightarrow{\mathrm{Fun}(-,-)}\mathrm{Cat}_∞$$ where $i$ is the functor induced by the group antihomomorphism sending $g$ to $g^{-1}$. This is just the classical functor category equipped with the conjugation action sending $F$ to $gFg^{-1}$.

Then, to get $G$-equivariant functors all you have to do is take homotopy fixed points (i.e the limit of the functor $BG\to\mathrm{Cat}_∞$ ): $$\mathrm{Fun}^G(\mathcal{C},\mathcal{D}):=\mathrm{Fun}(\mathcal{C},\mathcal{D})^{hG}\,.$$ So, morally, $G$-equivariant functors are just functors equipped with equivalences $F\to gFg^{-1}$ and all higher coherences needed. In fact you could spell out explicitely what the higher coherences are, but I'm uncertain this is at all useful in practice.

Let us see a bit how to get the two properties you are interested in.

Note that when they write $\mathcal{C}/G$ they probably mean the homotopy orbits, what's usually denoted $\mathcal{C}_{hG}$, i.e. the colimit of the functor $\mathcal{C}:BG\to \mathrm{Cat}_∞$. Then the first property is just the fact that $$\mathrm{Fun}(-,\mathcal{D}):\mathrm{Cat}_∞^{op}→\mathrm{Cat}_∞$$ commutes with limits. This is true because it is a right adjoint (in fact its own right adjoint, because adjunctions for controvariant functors are confusing).

Finally, the second statement follows from the first as you imagine, e.g. by using the description of colimits in $\mathrm{Cat}_∞$ in Higher Topos Theory, section 3.3.4 to show that $*_{hG}\cong BG$

Remark that everything we did respects equivalences pretty much by definition. In fact the language is cooked up so that we cannot say statements that are not invariant under equivalences.

A(n ∞-)category with $G$-action is just a functor $BG\to \mathrm{Cat}_∞$. Then, if $\mathcal{C},\mathcal{D}$ are (∞-)categories with $G$-action, we can get another (∞-)category with $G$ action $\mathrm{Fun}(\mathcal{C},\mathcal{D})$ by pairing them: $$\mathrm{Fun}(\mathcal{C},\mathcal{D}):BG\xrightarrow{(i,1)}BG^{op}\times BG\to \mathrm{Cat}_∞^{op}\times\mathrm{Cat}_∞\xrightarrow{\mathrm{Fun}(-,-)}\mathrm{Cat}_∞$$ where $i$ is the functor induced by the group antihomomorphism sending $g$ to $g^{-1}$. This is just the classical functor category equipped with the conjugation action sending $F$ to $gFg^{-1}$.

Then, to get $G$-equivariant functors all you have to do is take homotopy fixed points (i.e the limit of the functor $BG\to\mathrm{Cat}_∞$ ): $$\mathrm{Fun}^G(\mathcal{C},\mathcal{D}):=\mathrm{Fun}(\mathcal{C},\mathcal{D})^{hG}\,.$$ So, morally, $G$-equivariant functors are just functors equipped with equivalences $F\to gFg^{-1}$ and all higher coherences needed. In fact you could spell out explicitely what the higher coherences are, but I'm uncertain this is at all useful in practice.

Let us see a bit how to get the two properties you are interested in.

Note that when they write $\mathcal{C}/G$ they probably mean the homotopy orbits, what's usually denoted $\mathcal{C}_{hG}$, i.e. the colimit of the functor $\mathcal{C}:BG\to \mathrm{Cat}_∞$. Then the first property is just the fact that $$\mathrm{Fun}(-,\mathcal{D}):\mathrm{Cat}_∞^{op}→\mathrm{Cat}_∞$$ commutes with limits. This is true because it is a right adjoint (in fact its own right adjoint, because adjunctions for controvariant functors are confusing).

Finally, the second statement follows from the first as you imagine, e.g. by using the description of colimits in $\mathrm{Cat}_∞$ in Higher Topos Theory, section 3.3.4 to show that $*_{hG}\cong BG$

Remark that everything we did respects equivalences pretty much by definition. In fact the language is cooked up so that we cannot say statements that are not invariant under equivalences.

A(n ∞-)category with $G$-action is just a functor $BG\to \mathrm{Cat}_∞$. Then, if $\mathcal{C},\mathcal{D}$ are (∞-)categories with $G$-action, we can get another (∞-)category with $G$ action $\mathrm{Fun}(\mathcal{C},\mathcal{D})$ by pairing them: $$\mathrm{Fun}(\mathcal{C},\mathcal{D}):BG\xrightarrow{(1,i)}BG^{op}\times BG\to \mathrm{Cat}_∞^{op}\times\mathrm{Cat}_∞\xrightarrow{\mathrm{Fun}(-,-)}\mathrm{Cat}_∞$$ where $i$ is the functor induced by the group antihomomorphism sending $g$ to $g^{-1}$. This is just the classical functor category equipped with the conjugation action sending $F$ to $gFg^{-1}$.

Then, to get $G$-equivariant functors all you have to do is take homotopy fixed points (i.e the limit of the functor $BG\to\mathrm{Cat}_∞$ ): $$\mathrm{Fun}^G(\mathcal{C},\mathcal{D}):=\mathrm{Fun}(\mathcal{C},\mathcal{D})^{hG}\,.$$ So, morally, $G$-equivariant functors are just functors equipped with equivalences $F\to gFg^{-1}$ and all higher coherences needed.

Let us see a bit how to get the two properties you are interested in.

Note that when they write $\mathcal{C}/G$ they probably mean the homotopy orbits, what's usually denoted $\mathcal{C}_{hG}$, i.e. the colimit of the functor $\mathcal{C}:BG\to \mathrm{Cat}_∞$. Then the first property is just the fact that $$\mathrm{Fun}(-,\mathcal{D}):\mathrm{Cat}_∞^{op}→\mathrm{Cat}_∞$$ commutes with limits. This is true because it is a right adjoint (in fact its own right adjoint, because adjunctions for controvariant functors are confusing).

Finally, the second statement follows from the first as you imagine, e.g. by using the description of colimits in $\mathrm{Cat}_∞$ in Higher Topos Theory, section 3.3.4 to show that $*_{hG}\cong BG$

Remark that everything we did respects equivalences pretty much by definition. In fact the language is cooked up so that we cannot say statements that are not invariant under equivalences.

A(n ∞-)category with $G$-action is just a functor $BG\to \mathrm{Cat}_∞$. Then, if $\mathcal{C},\mathcal{D}$ are (∞-)categories with $G$-action, we can get another (∞-)category with $G$ action $\mathrm{Fun}(\mathcal{C},\mathcal{D})$ by pairing them: $$\mathrm{Fun}(\mathcal{C},\mathcal{D}):BG\xrightarrow{(1,i)}BG^{op}\times BG\to \mathrm{Cat}_∞^{op}\times\mathrm{Cat}_∞\xrightarrow{\mathrm{Fun}(-,-)}\mathrm{Cat}_∞$$ where $i$ is the functor induced by the group antihomomorphism sending $g$ to $g^{-1}$. This is just the classical functor category equipped with the conjugation action sending $F$ to $gFg^{-1}$.

Then, to get $G$-equivariant functors all you have to do is take homotopy fixed points (i.e the limit of the functor $BG\to\mathrm{Cat}_∞$ ): $$\mathrm{Fun}^G(\mathcal{C},\mathcal{D}):=\mathrm{Fun}(\mathcal{C},\mathcal{D})^{hG}\,.$$ So, morally, $G$-equivariant functors are just functors equipped with equivalences $F\to gFg^{-1}$ and all higher coherences needed. In fact you could spell out explicitely what the higher coherences are, but I'm uncertain this is at all useful in practice.

Let us see a bit how to get the two properties you are interested in.

Note that when they write $\mathcal{C}/G$ they probably mean the homotopy orbits, what's usually denoted $\mathcal{C}_{hG}$, i.e. the colimit of the functor $\mathcal{C}:BG\to \mathrm{Cat}_∞$. Then the first property is just the fact that $$\mathrm{Fun}(-,\mathcal{D}):\mathrm{Cat}_∞^{op}→\mathrm{Cat}_∞$$ commutes with limits. This is true because it is a right adjoint (in fact its own right adjoint, because adjunctions for controvariant functors are confusing).

Finally, the second statement follows from the first as you imagine, e.g. by using the description of colimits in $\mathrm{Cat}_∞$ in Higher Topos Theory, section 3.3.4 to show that $*_{hG}\cong BG$

Remark that everything we did respects equivalences pretty much by definition. In fact the language is cooked up so that we cannot say statements that are not invariant under equivalences.