what eaxactly is it and what does it do/help?

http://www.rifleshootermag.com/gunsmithing/bedding_0304/

best of luck

Glass bedding basically makes your stock fit your action. When you shoot, it dampens the vibrations and harmonics or makes them consistent. It also keeps the action solidly mountedso it doens't move around in the shot.

When done right glass bedding will go a long ways twards insuring your action sits in the stock tension free. Also the bedding will insure that the action will be located near exactly the same each time one takes the rifle down & puts her back together.

This sight providesis one of my favorit explinations of glass bedding. http://www.6mmbr.com/pillarbedding.html

AlthoughI do like the sight provided above as also.

These guys have you covered pretty well.I would just add that it helps eliminate forces from the stock being transferred to the action.