I cast my first spell two nights ago, and I don't know if it worked or not. How long does this stuff take, anyway?
Depending on who you ask, the answer is usually anywhere from a few days to a couple of weeks. In nearly all Wiccan and Pagan traditions, the general rule of thumb is that if you haven't seen something begin to manifest within four weeks -- one lunar cycle -- then you may need to revisit your working. In other traditions, particularly in Hoodoo and rootwork, a spell is designed to be worked over a specific period of time, and then results should appear within a designated amount of time after the working is complete.
Bear in mind that sometimes you get results that aren't what you were expecting, and in that case, you might need to evaluate the method you used to cast the spell in the first place.
A good idea is to keep a magical journal of some sort. Record what you did, when you did it, what the circumstances were, etc. Jot down everything that happens, so that you can look back later and see if it has begun to manifest.