Scores are ranked from 5 to 1:
5 = Extremely well-qualified
4 = Well-qualified
3 = Qualified
2 = Possibly Qualified
1 = No recommendation

Usually only scores greater than or equal to 3 are accepted by colleges as passing; more selective colleges may give credit only for 4's or 5's or perhaps even not at all. Most colleges, however, will allow students to take more advanced course work through demonstrated proficiency in the AP exams. It's also important to know that scores are evaluated on steep curves so that a 68% raw on the Calculus BC exam may be the lower bound for a 5 (these exams are challenging!).

Throughout high school, students sometimes feel a need to take more AP classes/exams in order to better their chances in college admissions. What's important to realize, however, is that colleges do not emphasize AP exams nearly as much as standardized tests and that colleges will want to see you take APs (and do well on them) in areas you care about. Taking more advanced classes is almost always good if you really like the subject and want to delve in deep, whether to prepare for a contest or to just enjoy.

Aside from gaining college credit, there are certain awards given for performing well on Advanced Placement exams including the AP awards administered by the College Board and the Siemens AP awards for proficiency in the science APs.

A list of the different subjects covered by AP tests is available here.