Take a look at this six and half minute video of how to utilise the Access DLookup function using a little of Access VBA code too (not too difficult but necessary in this example).
Microsoft Access Database: Access DLookup Function Example with Access VBA
Of course you do not have to use Access VBA code when applying the Access DLookup function. Instead, you can populate fields by using a calculation or auto-lookup query instead.
With the calculation method however, this is just an expression and will not be updatable should data in fields need to be edited.
Take a look at my eBook on More Access Database Queries to learn about the ‘Auto Lookup’ query and other more adavnced techniques.