Add the group connection on hamachi:
Connection :Garry's mod Hamachi servers
Password : gmod

Tutorial how to use hamachi:
You can create or mount connections, for make that go to the triangle icon : Crate connection or join one.. For join write the connection and password. Like the one in the top. To create a server you need to configurate hamachi, Go to Control panel, go to the icon of a world and two computers, go to the icon of a world and a plug and go do advanced: Advanced Settings:
You will see Hamachi and other things with 2 green arrows. Select hamachi and put it on the top with green arrow. Done! now you can make your hamachi server!