Given a quasi-projective $X$ variety that is the union of two affines $\text{Spec(A)}$, $\text{Spec(B)}$ with intersection $\text{Spec}(C)$. Let $f\in C$. Then $\text{Spec}(C_f)$ is an open in both of $\text{Spec(A)}$ and $\text{Spec(B)}$. What is the gluing of $\text{Spec(A)}$, $\text{Spec(B)}$ along $\text{Spec}(C_f)$ and its relation to $X$? I can only imagine this object very intuitively and I'm not sure if it is correct or not. It seems to me this is not a separated scheme and it resembles $X$ with double the portion of zeros of $f$ that are in $\text{Spec}(C)$. Specially it seems to me there are two maps from $X$ to this scheme. Is it possibile to make these more clear in case they are true?