Mostly yes, depends on a few factors. What happened when you tried it? Sometimes you need a second table occurrence. Can you post a sample file with some dummy records, or some screen shots?
A portal displays records based on a relationship (join). If table A is related to table C then yes table A could have a portal based on items in table C. It's a little bit more complicated when you have a many to many relationship. A couple of examples for a relationship or portal. You have a customer and then you keep notes on this customer. If you had a single note field your notes field would could filled up fast and then it would be hard to date each note. You would have a related note table. Then you could have zero notes for a customer or thousands of notes. Much easier to track. The Invoice starter solution would be a good example of a many to many relationship. You have many invoices with line items related to that invoice and that invoice is related to products table with many products. I would not start on many-to-many relationship until I got the one to many relationship down.
Global fields can be displayed on any table without a relationship, but that is a different subject.
If you have this relationship:
A portal to C may be placed on a layout based on A. But it will not show any records without join records existing in Table B that link the current record in A to records in C.
This can be useful in some cases where you just want to see the records from C that are linked to the current A table record.
But it is often better to use a portal based on B that includes fields from C in the portal row. Such a portal makes it easier to add new links that connect the current record in A to existing records in C.
The standard invoices layout--such as the starter solutions that come with versions 11, 12 and 13 use this method on the invoices data entry layouts to list the individual items purchased on a given layout. Fields from the Products table (table C) can, if desired be included in the rows of this portal to show data about the product selected for that row of the portal.