Best way to add data into database

I would like to have multiple inserts into one row on a table in the database, for example.
Modules (1,2,3,4,5)

Obviously when it is first put in it would only contain;
Modules (1)
so when they complete a module the I want to add the next module number.

What is the best way to get this inserted and also what is the best way to separate it when a query is made.
Any help would be appreciated.