How do you plant a bomb in Counter-Strike Condition Zero?

It should be the same concept for all the Counter Strike versions.

You first have to obtain a bomb; either by getting in when you spawn, picking it up from the ground, or having a teammate toss it to you.

Then, all you have to do is find a bomb site (marked usually with an "A" or "B" on the radar).

Once you get in range of the bomb site, press the number "5" on your keyboard and this will take out your C4 bomb.

Hold left-click, your guy will start pressing numbers. Don't let go of left-click until you see the bomb has been planted on the ground.

Usually what's followed is your radio says "Bomb is planted" or something similar.