This question is actually a little bit vague. Anyway, I hope you can find the following answer useful.
One of the more general results about linear systems of curves on surfaces is the following theorem, proven by I. Reider using rank $2$ vector bundles techniques:
Theorem (Reider). Let $X$ be an algebraic surface, and $D$ be a nef and big divisor on $X$. Then
- If $D^2 \geq 5$ and $x$ is a base point of $|K_X+D|$, then there exists a curve $E$ on $X$ with $x \in \operatorname{Supp} E$ such that either $DE=0$ and $E^2=-1$ or $DE=1$ and $E^2=0$.
- If $D^2 \geq 10$ and $x,y$ are two points, possibly infinitely near, such that $|K_X + D|$ does not separate $x$ and $y$, then there exists a curve $E$ on $X$ such that $x,y \in \operatorname{Supp} E$ such that either $DE=0$ and $E^2=-1$ or $-2$ or $DE=1$ and $E^2=0$ or $1$ or $DE=2$ and $E^2=0$.
This result has many important consequences. For instance, it can be used to deduce Bombieri's theorem for pluricanonical systems (if $X$ is a surface of general type, then the $5$-canonical map is a birational morphism of $X$ onto its canonical model $X^{\textrm{can}}$.
Another application is the following result for abelian surfaces:
Theorem. Suppose $D$ is an ample line bundle of type $(1,d)$, with $d \geq 5$, on an abelian surface $X$. Then the morphism $$\varphi_D \colon X \to \mathbb{P}^{d-1}$$ is an embedding if and only if there is no elliptic curve $E$ on $X$ with $ED=2$.