1994 Mazda B4000 4wd problem

My friend recently bought a 1994 Mazda B4000 extended cad w/4wd. She said that the 4wd will not work. She turned the 4wd knobs on the wheels to the lock position - heard a click when she put it on "free" but not when she put it on "lock". She said there are 3? buttons near the floor on the driver's side of the truck but she does not know exactly what they are for and was not told how to use them buy the seller. I think the buttons have something to do with the 4wd but she said there is nothing in the manual concerning these buttons and nothing on the buttons to identify them. Can you tell me what these buttons are for and how to set the 4wd so I can email her and give her an idea of what to do? Thank you.