Checkbox to SQL to Checkbox

I have the following situation: A company creates 5 stores on my website, one after another. The company then decides to add a new product and in the addproduct.php page the company gets shown a checkbox list of the 5 stores it has created before, so the company can check which store should the product go online in. So my question is - how do I fetch (from SQL) the 5 stores the company has in the addproduct.php page and then how to process their selecton (checked checkboxes) and store the selection in SQL. Seems so confusing to me. I read somewhere that I should use implode() and then explode() or serialize() and unserialize() but that seems too confusing to me.

BTW the checkboxes should containt the address of the stores (each created from a page addstore.php and stored as store_address in SQL).

HUGE thanks in advance!