Populate a second combo box based upon the first one....

Greetings

I'm new to the forum and learning a lot from all your posts, thank you for that if nothing else becomes of this request. I would like to understand how to fill a second combo box based on the selection of the first one. For example if I select a part in column B as 0005-2431 (which there are two entries) I would like the second combo box to show me the information in column P. Any help on the coding would be greatly appreciated....

Thanks
Bob