Saving data to multiple tables

I have 2 tables Users (for logging in) & Partners when creating a signup form I would like to be able to either add all the data on 1 forms

User Name, Email Password ect for users table
Partner Name, user_id etc for the partners table all in one form?

or how to do I pass the id of the newly created user to the partner form for the user_id?



You don’t need to. If your associations are set up correctly, and fields named to match, then just patch and save the user entity, and everything will work out right for the partner. The Saving Associations section explains this, and includes a link to how to build your form.