There are two basic ways to set up an "OR" relationship in FileMaker:
a) Put multiple matching values in the same field separated by returns. If you put the following IDs into a single text field:
The record with this match field can match to records in the related table with values of 3 or 40 or 5000...
b) use an intermediary "join table".
Accounts::__pkAccountID = Account_Note::_fkAccountID
Notes::__pkNoteID = Account_Note::_fkNoteID
Using same data from a), you have three records in Account_note, one with an account id of 3 one with 40 and one with 500. All three of these records would have the same NoteID and thus would all link to the same record in Notes.