Instructions
Pick up the Long Jump Module by walking over it. Depending on the circumstances surrounding your acquisition of this device, it may be on the ground, on a pedestal or on a platform by itself. According to the "Half Life" wiki, you will hear the HEV suit say ̶0;Power Movement Assist Activated̶1; indicating that the power up is ready to go.
Move forward, press crouch and then press jump simultaneously. Timing is a factor, but the timing is not too strict. Your fingers should tap the crouch and jump keys in rapid succession, making sure to land on crouch before you press jump.
Practice this move a few times in the Black Mesa Hazard Course. The single player game puts players into situations where mastery of the Long Jump Module will greatly increase chances of survival, so the Hazard Course is ideal for familiarizing yourself with the basics.