nedfig,
The process is probably a little too much to explain on a bulletin board post, though some may try. Bedding a rifle is a trick that sets the action to the stock in such a way as to remove as many variations as possible from the physical interface between them (action-to-stock). It usually is an opportunity to make whatever modifications are necessary to free-float the barrel, if you think it is a good thing to do. There are pros and cons.
Bedding lays in a layer of epoxy-like material (see Acra-Glass in Brownell's) applied in the action area of the stock, that provides a consistent surface against which to mount the action.
Bedding permits torqueing the action to the stock to a specified value which is repeatable. Repeatable is important to accuracy. The action-to-stock interface contorting and shifting (because of humidity, handling, firing and time) is one of the big enemies of accuracy. Bedding helps correct that. The effectiveness of bedding is also debatable. However, it is generally accepted as a good thing to do.
Good quality synthetic stocks, like McMillan and H&S Precision do not require bedding, as they already have a good bedding surface aginst which to torque the action.