Newbie Question.. User groups MYSQL

[ColinSealeaf]

Hi there,

I am totally new to PHP. I have been an Network/Infrastructure Engineer for 9 years and am now setting up a website.

After reading the tutorial on here I feel underdstand the user creation/Password creation-validation stuff but this is what I need:

1 User to login
2 User to create a group or join an exisiting group. (simple data will be held on per person in the group)
3 User can only exist to one group.
4 How do I secure the database down so the user can only modify their data??

I am hoping that the groups will reach a large number. Don't know if thia had any impact.

Any help would be gratefully appreciated.

If I can help anyone with server/infrastructure stuff pls let me know!!

Thanks very much
Col