The Buk missile and its launcher, the M1-2 system, is clearly described in Wikipedia, "Buk Missile System."
It is a mobile system, with both aquisition and targeting radar, a command unit, missile launchers and logistics element, mounted on a tracked vehicle.
"In general, the system identifies potential targets (radar), selects a particular target (command), fires a missile (launcher) at the target, and resupplies the system (logistics)."
A proximity fuse aboard the missile determines when it will detonate