To quickly find and join your Unturned server, please follow the steps in this guide.
On the main menu screen, click the "Play" button.
On the following screen, click the button "Connect", with the icon of a plug next to it.
and you will see this screen next...
The background makes it a little hard to read, so here's a closeup view of the fields
In the topmost box that is circled in red, enter your Unturned server's IP address. You will find this on the "overview" tab of the Nodecraft server control panel. The IP address is generally 4 groups of numbers, separated by three periods. Type it into the top box.
If you have a password set on your Unturned server, you will need to enter that in the password box too.
Connect, and you will join your server!