i have a detonator and i have dynamite and a landmine how do i combine the detonar with the dynamite or the landmine?? i am on the ps3

You need to find C4 that can be found on black mountain and other places with explosive crates.

Yes a detonator only works for the placed C4.

You need to drop it, or throw it into position.
Then you equip the detonator, press the fire button on yuor mouse / gamepad.
This will make it go boom, be advised it is highly dangerous don't stand close when you press fire.