what is bead blasting

Its where you take small beads and "shoot" them on an object under high pressure. Kinda like pressure washing with water, except with beads. The beads under such pressure act as an abrasive and remove any coatings etc on the object being blasted. The higher the pressure, the faster the beads are shot out, and the harsher their abrasive action is. You can also buy different grit media to control abrasivness as well. If your familiar with sandblasting, its the same thing but different media being used.

so when you bead blast a minifold it cleans it?

Yep, removes any rust, paint, etc and leaves you with bare metal ready to accept a finish.

You need to clean the manifold carefully after bead blasting.
Use soap & lots of water, then blow-off with compressed air.
A bead blaster uses small glass beads, they can hurt the valves and cylinders if they get into the engine.
DD