Bolt cutters are easy to use, but can take a lot of strength to open, especially if rusty. Most people will probably use bolt cutters only a couple of times in their lives, such as when they've lost the keys to their bike or storage unit lock.
First, check the safety latch.
If the safety latch is on, open it by twisting it to the left.
If the bolt cutters still don't open, get a can of WD-40, which can be found at any hardware store and some drug stores.
Spray liberal amounts of WD-40 on the hinge connecting the two sides of the bolt cutters.
Pull the bolt cutters apart.