The 5 Board Press, along with the 4 Board Press, is one of of the best ways to increase lockout strength for your bench press.
To perform a 5 Board Press, place 5 2x6 boards on your chest, bring the bar into the boards, let it sink into the boards (slightly) and press back up. Make sure that your flare your elbows at the top to maximize your lockout strength. This is because your lockout position when doing the 5 Board Press has to mirror your actual bench press.
Don't be alarmed if your 5 Board Press is not the same as your regular bench press. Many times people will be lower in this movement than there shirted bench because of lack of speed/momentum that they get when they perform a full-range movement. The point is to strengthen your lockout.
This is best performed as a 2nd exercise (supplemental lift) for multiple sets of 3-5 reps. If you are a raw lifter, this lift may not be a staple in your training arsenal. This lift is especially important if you do compete with a bench shirt.