Depending on the AP, the department’s policies, and your score, AP’s can a) count towards credit for a major, b) count as general education requirements, or c) allow you to skip introductory material, but not count for credit. If it counts as credit for your major, it will usually also allow you to skip. Policies, especially towards gen-ed credit, vary a lot by school. My school gave me credit but they’re just raw credits, they don’t count toward any requirements, either gen-ed or major, so I will essentially just be graduating with random credits on my transcript. I could theoretically take a semester of three classes at some point but it’s hard to finish all my requirements doing that. On the other hand, I have a friend with a huge ROTC time commitment who judiciously chooses to take semesters with three classes in order to give her more time to study for her toughest courses, so they can be useful.
You’re a freshman and you’re going to be changing a lot in the next four years, but assuming you do end up majoring in science or engineering, the most useful AP to plan to take is calculus (AB is usually equivalent to Calc 1, BC to Calc 2). The vast majority of schools grant placement for it. (Note that your score does matter - sometimes a 3 is acceptable, but more often a 4 or a 5 will get you placement. Some schools require a 5.)
If you’re waffling about whether or not to take AP Human Geography, don’t let the college credit you may or may not get be the deciding factor. It’s a really interesting class which teaches you a lot about the world; I took it and I think it’s worth it, but if it sounds terribly boring don’t force yourself to take it just because it’s an AP.