Pos screen Grids is the name we give to popup options or other layers of buttons. This can be accessed by going to Setup > Pos Screen > Pos Screen Grids.
To create a grid press add down the bottom right hand screen and type the name you would like the grid to be called, once done that close out of the add screen, select the grid and press items.
In here you can modify the grid exactly the same you would a button and also link this grid to another grid if needed.
There is some other grid functionality however if you have any questions please feel free to contact our office