They'll probably be some GUI tool for creating new users but I don't know what it is in debian. The command line method is with useradd command
Groups you belong to are defined in /etc/group so you'll need to look at that and modify as appropriate.
If you want to copy all your config settings then the easiest way is once you've created the new user, become root, change in to the new user's home directory then do
Code:
$ cp -r /home/oldusercode/.[a-zA-Z0-9]* .
$ chown -R newusercode .*
cp copies file, chown sets ownership.