Sorry, I hope we are understanding each other. I may not have explained it well. Also, please keep in mind, I am a real novice when it comes to databases, etc.
So yes, I am expecting to have two relations (this was just an example but it's quite analogous to what I am attempting). The first relation is employees and the attributes are id (ie the mandatory one created for all relations), employee_id (our existing ids), last_name, and first_name.
The second relation orders will have many attributes (like start_date, finish_date, various materials, etc), and one of those attributes is assigned_employee.
I am making a form to add new records to the orders relations, and I am hoping that when a user clicks on that particular field, it will let them directly enter an employee_id, if they know it, but also provide the option for a dropdown list populated from the employees relation. Of course, some other design that is straightforward is also acceptable.
What I have done is create a form and selected the orders relation. That gave me the many attributes of that relation as options to use as fields on the form, I see there is a join button, but that doesn't let me add anything, it just gives me a list of one "select relation to join". There is no problem with the current design so long as the user knows the employee_id (which actually normally they will), so what I need is a reasonably elegant soluton for when the user doesn't know the id (like it's a new employee's for example). I hope that explains what I am trying to do.
Just to be clear in terms of our specific situation, we have around 40 employees and on this form I am expecting users will usually be assigning themselves (and they already know their own numbers) to this field. They will be occasionally assigning other employees too however.