access-database-training - Showing info from another form

I'm rebuilding a database and want to replicate something it does in another form. In a nutshell, the form has a lookup combo box which contains details from another table, so when you enter a piece of equipment you can choose from the combo box what kind of equipment it is. The bit that's puzzling me is that once you've chosen what you want from the pop-up in the combo box, it displays info from the line you chose in extra fields on the form. How is it doing this?? In design view, the fields that shows this info contain:

=[ComboItemKey].[Column](4)

and

=([ComboItemKey].[Column](1))+(" ")+([ComboItemKey].[Column](2))

I want to replicate this elsewhere in other forms but can't work out what this bit of code is doing/pointing at - can anyone help me out or suggest anything?