This is called a conditional value list.
Download this free file: "Adventures in FileMaking #1 - Conditional Value Lists". In it, you'll find 10 different ways to set up a conditional value list. The "basic conditional value list" example should be exactly what you need here.
You might want to try this for a very Basic conditional Value List:
You should have 3 Tables:
- Table A is your Data entry form which has the fields Brand and Model at least
- Table B "Brand" for all the Brands
- Table C "Models" for Brands and Models
Then your are linking Table A with Table C thru the "Brand" field:
Next you generate two value lists:
- One value list based on the Brands table
- One value list based on the "Models" table, showing the Model-field of this table and you click "showing only values starting with "Data entry form"
The "Brands" Value list you can also use for entering for Model-Data - this ensures, that you don't enter wrong Brands or spelling on Brands.
Now you define in your data entry form the Brand value list on your brand data field and your Model value list on your Model data field
Next things to do: Add IDs to your tables, so that changes in Brand names and Model names will be automatically reflected in your data entry form (some more linkage and definition is required)