do i upvote or downvote?

new to reddit and im not sure what the culture is with upvoting/downvoting. Do i upvote if i like it, and downvote if i dont? Because there are posts that dont have good content (abuse, etc) but i liked the.. post i guess? i see ppl downvote or upvote these types of posts and honestly i don't know. Wanna upvote because i enjoyed reading it, but wanna downvote because everyone else is or because the content isnt good. Idk.