Tags from form

[eluser]someone [/eluser]
Hello!

I have some problem with field in form. This field is tags, where I would like to get tags from this form. If I enter in it: tag1, tag2, something, someone and in my tags already are tag1 and something, but not other to do next. Words which exist must get some id (from database), and words which are not already in database, must be entered to database and get id. Then I would like that application insert those id in database.

How to do this?

Thanks! :-)

EDIT: Structure of getting this in database -> http://i.imgur.com/cmUON.png .