Generally the following occurs:
cp_awesomeface_a# -- a means Alpha. Most mappers map with dev textures. Focusing on layout. The dev textures result in people not complaining about detailing, and instead complain about "Man, this path here is useless," or "This is so engineer-friendly," etc.
cp_awesomeface_b# -- b means Beta. Most mappers remove dev textures by now. Focusing on detailing.
cp_awesomeface_rc# -- rc means Release Candidate. The map is essentially finished. Generally, once a map is rc, it won't be updated again until many months or a year later, when the few remaining issues are fixed (for example, Meridian).
If you've seen _test or _c, those are for test versions and contest versions. Generally, don't use either.
Some people don't follow that exact roll, though. SWATY tends to not release alphas. I personally detail in alphas, because I'm too OCD to have dev textures. Supertoaster uses very mild detailing in his alphas instead of dev textures since he thinks they "look like poop." You don't have to follow that exact approach above, but for a new mapper, START like that. If you learn that dev textures are standing in your way, take an extra month to detail and release a detailed alpha - just don't expect it to be perfect and expect to have to slpend the time to change the detailing you've done to fix any layout issues.