Using a list to validate options on another list

What you seek is called a cascading drop-down list. Do a web search for it. The method you are most likely to find involves setting up the lists you want for the first selection across the columns and the items for the selection in the rows under it, and then using MATCH and OFFSET.

I have a somewhat different approach which can cascade any number of levels. If the data in the lower levels of the cascade are unique, you can use the non-vba method. Otherwise, the vba method should work in all cases.
http://www.utteraccess.com/wiki/Casc..._%28Non-VBA%29 (Non VBA)
http://www.utteraccess.com/wiki/Casc...ists_%28VBA%29

However, there may be an even simpler solution: look up Slicers. They are easy to implement, and they are self-cascading.

Here is an example using slicers. The data in the table in columns A & B set the "rules." I made pivot tables against this table with the filters being First Choice and Second Choice. This isn't necessary, but if you want to use the selection anywhere, there's a cell that you can reference.

So do an example: Select A from the First Choice Slicer. Notice that the second choice slicer has some selections already grayed out and that Cell F1 shows the selection. Select one of the available choices and it will appear in cell F4.

Clear both slicers by clicking on the funnel icon on the upper right. The pivot table selections revert to (All).

Now select 3 as the second choice. 3 is set in Cell F4. Note now that only B is available in the first choice slicer. This is because ONLY B has a second choice equal to 3.

Slicers work both ways.