Database link'n'joining Qs

Help requested : Linking & Joining Tables for lookup ...

When designing a new form some questions are of greatest interest
for many Delphi developers, MAST application uses some of these techniques :

Form layout :

EmplNo
----------------------
I      TDBEdit1      I
----------------------

Name                               Adresse
----------------------             ---------------------------------
I      TDBEdit2      I             I      TDBEdit3                 I
----------------------             ---------------------------------

ZIP                                     State
-----------------------    ----------   -------------------
I      TDBEdit4       I    I SEEK   I   I      TDBEdit5   I
-----------------------    ----------   -------------------

First how to question :
Type the employment number in TBEdit1, when leaving this edit field, the Name
and
Adress field will be filled in automatically if given emplmnt number exists in
the
Employer.DB table.
Wanted step by step instruction how to do this.

Second how to Q :
Type the ZIP code in the TDBEdit4 field and the corresponding State will
automatically show in TDBEdit5 field when leaving the TDBEdit4 field.
The Zip and state info is taken from the table ZIPCODE.DB  to update
the table EMPLOYER.DB which is shown in the form above.
Please provide step by step how to.

Third how to Q:
By pressing the seek speedbutton, choose from lookup table (ZIPCODE.DB)
the wanted code and the two corresponding fields in this form(above) will be
updated.
Please provide step by step how to.

Sincerely Geir.