how do i run a custom function from a displayed form

Hi

I have built a custom module which displays entries from the database to the site administrator, i have now created a mod. file for the module to display the form to site users.. once the user completes the form it should then add the details to the database. How do i specify the function the users form needs to run to add the information to the database?

I have found that it is possible to do this by placing the php in its own template file with allowed php and then linking the form action to this template… is this the only way?