Heres a small guide that should help.
First thing to do is open your navicat and then double click on your database such as this first picture
Next you will right click on your database name and choose "Manage Users" Just like the following
Next you will click "Add User"
[img]http://img187.imageshack.us/my.php?image=43525374hg7.png[img]
The next thing to do is fill out the new area.
In the Username field put their username to log in.
In the host put their ip, If your using hamachi put their hamachi ip here.
In the password field put their password.
In the repeat password, put their password again.
Then you click ok and it adds the user
Next you will need to give them permissions.
On the left you will see the usernames that have access to your database, if you single left click on the new one, you will see all the fields to the right are unchecked. Check the ones that you want to give them permission for. Then hit save
[img]http://img187.imageshack.us/img187/493/34277154hl0.png[img]
Now for them to connect to your db, they will need to get navicat and make a new connection:
1: In the Label put anything to name your server.
2: In the host, they need to put your ip or hamachi ip to connect to your server.
3: In the username, they will enter the username you made earlier and then for the password its the one you created.
4. Next thing to do is test the connection and make sure it works. If it does then they have access, if it doesn't recheck all the other examples. Good luck.