Point of sale display of grids

Hi, 

I am developing a POS system. But I am a bit confused about the Grid system. Forgive me if I sound foolish,

but usually in POS systems, the item code will be scanned or typed in a textbox and it will search from a pre entered list of items in an entity to display the price etc. But what I am a bit confused is, how to add that searched data of the item to a grid list below. And keep it on that grid as the next item is searched and added the same way. And after finished adding, we have to check out, means commit that data to an entity?? 

Please help, any help is useful.

Dilan