Get a stockpot and fill it with a generous amount of water (you can adjust this depending on how many breasts you're boiling).
Bring it to a boil.
Add chicken breasts.
Check for doneness after 12 or so minutes. (I'd suggest investing in a pair of tongs for that. Using the tongs, take one of the larger breasts out and cut it open with a knife - if it's still pink you know that you have keep boiling 'em. If it's all white, you can take it and all smaller breasts out, then check one of the breasts that left. Repeat as necessary til all breasts are out of the water.) Depending on the amount of chicken you put into the pot it may take the water a little longer to resume boiling.
I boil a lot because I use them for chicken salad, sandwiches and other meals throughout the week. (Especially when pressed for time and I want something healthy). When done correctly the insides will be moist and tender, with a wonderful taste to them. I typically combine this with brown rice cooked in nonfat chicken broth and blanched veggies for a healthy meal.