You don't open tables in FileMaker. You do open records for a given table for editing.
It would depend on details you haven't shared as to the best method for what you want to do. Manually edit them? Modify them with a script?
The most straight forward method is to navigate to a layout based on a Tutorial: What are Table Occurrences? (Selected in "Show Records From" in Layout Setup...) for that table. You can perform a find or use Go TO Related records if you want to modify existing records, you can use new record to add new records and delete record to delete a record. And this can be done manually or with a script. The basic concept is the same either way.
But this is not the only way you can do that. If there is a valid relationship to from the current layout's table occurrence to an occurrence of the table where you want to edit data, you may be able to edit data directly in that other table. If you are editing data manually, this is most frequently accomplished via a portal. If you are using a script to edit the data this approach is still possible, but it is often better to freeze the window, pull up the desired records on a layout based on the related table, edit them and then return to the original layout.
And note that if you want to manually edit data in a table, you can use either layout or table view on a layout based on the desired table that allows you to see and work with multiple records at the same time.