The basic requirements:
1. Each table must have a field that contains a value identical to the value in the other table's 'match' field. These fields are often called "keys". Table1:: primarykey would have the same value in it as Table2::foreignkey. It is these values being identical that lets FMP know which records should be related to one another.
2. There must be a relationship set up between these tables. File>Manage>Database>relationships tab. drag Table1:: pkey to Table2::fkey and you'll see an [=] symbol appear with a line connecting these tables.
3. The portal must be set up to show records from Table2 (Portal Setup...) assuming the layout itself is based on Table1.
If any of these is missing, it won't work properly.
read up on Table relationships, relationship keys and portals in the FMP help index. Give it another try, and let us know what you're seeing.