Hi there

I am trying to understand how databases work.
I have been reading lots of stuff in the net and I starting to understand.... but there are some things I cannot find out.....
So I decided to try here.... hope someone can help.

I am trying to make a site which has a product database.... Which I can do already up and working fine.... but I now need to expand my database with many different tables to store all the different types of data I need.... primarily....user info, product info, manufacturer info,then more complex tables to enable me to intergrate a shopping cart..... eventually.

SO
One question..... maybe two.....

Say I have a product table linked to the manufacturer table.

from the pdt_man field in the product table linked to the primary id id_man in the manufacturer table

I asume that the reason for having two tables is to not have to repeat the same info over and over again and be able to update easily etc....

So.....
How do I insert data in to two tables? ..... I know to use the insert into two tables wizard... but what if more than two tables? Do I use the many to many tool?

And..... When I add a new product... from an insert record form... then I need to put the manufacturer how does my database know that the manufacturer I write is the same as one already in my database or a new one......

Do I have to create a dropdown menu in my form to choose from manufacturers already in my database..... and another field to add a new manufacturer..?

It is driving me crazy thinking about how these tables link together

Any help would be greatly appreciated.....
Any links, books, anything that would help me understand the database structure I need to set up a online store.... most importantly how the tables relat to each other....

Thanks
Have a nice day