What I would like to do to help you understand better is the following:
I have a client table with the following fields:
IdCliente int not null primary key auto_increment;
Nombre varcjar;
Apellido varchar;
Direccion varchar;
Telefono varchar;
An invoice table:
IdFactura int not null primary key auto_increment;
Tipo char;
Fecha datetime;
And a customer_table table:
IdCliente
IdFactura
Then what I would like first is to have the client appear in the form, name and surname that would be taken from the customer table and then the amount of invoices that would be taken from some form of invoices. And apart from that, you can insert, update and delete these data. Thank you very much