I'd ask someone in your store specifically because it varies state to state, but here the following is how it works:
Shifts under 4 hours get no break.
4 hour shifts get 1 15-minute break.
6 hour shifts get a break and a 30 minute meal.
7 hour shifts (in the building for 7 hours, not 7.5, the 7 includes your lunch, gets a second break.
10 hour shifts receive a third break.
Meals must be taken no more than 6 hours apart. ie. Let's say you are scheduled to work 8:00-2:00. You'd get a break and a lunch. Let's say you take your lunch at 12:00. You later are asked to stay till 8:00 PM. You could have worked 8:00 till 8:00 with one lunch if it had been taken dead center in the middle of your shift, since you'd have 5.75 hours on either side of it, but since you took a lunch at 12:00 already you will now require a second lunch sometime before 6:30.