Even with custom tables this will work.
Take the following example relationship:
On the 'My Custom Table' record you have a related list and that related list's name is My Custom Child Table > My Custom Table.
When you click new in the related list, the Parent field on the My Custom Child Table will automatically be populated.
To see an example of this in an OOTB incident record, select the 'Child Incidents' Related list and click New. On the record that shows up, you'll see that the 'Parent incident' field is pre-populated with parent record you've just come from.
As I said above, this is just standard functionality across the platform, regardless of whether you are using custom tables or not. Full documentation on Related Lists can be seen here.
Callum
