As Nitro said

Look under the hood near the master cylinder for a solenoid looking part that has a brake line going into it and out of it. The solenoid is about 3 inches in diameter and 3 or 4 inches long.

The line lock is activated by depressing the brake pedal and then pushing the switch button on the shifter. This button engages the solenoid to hold the pressure in the front brakes. Next, release the brake pedal while keeping the switch depressed. Now you have the front brakes locked up until you release the button. The back brakes unlock when you take your foot off the pedal so you can hold the car from rolling by the front brakes.

If you let off of the button at any time, the front brakes release normally. If you push the button and then push the brake pedal, the front brakes dont work because the solenoid has closed the port.

But then, the button is probably for looks only and isnt connected to anything!!