I'm not sure what you want to know.
If you put a combobox in your spreadsheet, rick-click on it and you'll see "Format Control" on the pop-up menu.
Select it, and head to the Control tab, where you'll see the various controls for this box. For example, you may want someone to choose from one of 50 states; write the 50 states down a column, and then when you set up your combobox, you'll set the input range to pick up the range that contains the states; now, when someone clicks on the combobox, they can select one of the states when it pulls down.
There are other fun things you can do with comboboxes, but let me know if this is in the direction of info you needed to begin with.