This one shouldn’t be that difficult.
I’ll assume you want to use 2 combo boxes, with the first selecting a category and the 2nd the lookup value. (You can’t do this in 1 combo with multiple fields – at least not without some fancy VBA code).
Ok, you have combo1 and combo2. Place them on a form
In combo1 – set the Row Source value to the query from the first table: “Select fieldname from tablename, order by whatever”
In combo2 – set the Row Source value to a new query that references the first, using this syntax: “Select lookupfieldname from lookupchildtable where lookupparentid = ” & [forms]![yourformname]![combo1]
create an afterupdate event for combo1. Choose code builder
Your code should look like this
Private Sub Combo1_AfterUpdate()
That’s it. Now, whenever you change a value in combo1, only the child values relating to that category will show in combo2.