You should have really searched this, but I'll give you a little info because I'm nice.
1. At Apple.com, it says that the battery can last up to six hours, but users will rarely get this much. With standard internet usage, a word document, and maybe iTunes, most users report somewhere between 3-4 hours (it will vary on how bright your screen is and how loud your speakers are, along with how many cycles your battery has been through).
2. The macbooks have good battery life in comparison to most PC laptops of their size, so don't sweat it.
3. Be sure to maintain your battery so that it will keep giving you good battery life. Apple will tell you how to do that.
4. Be sure to calibrate about once a month so that your computer gives you an accurate readout.