First, go to the data editor and go to Races.
Then, look for the field Show Resource. Enable Terrazine/Custom Resource for the race you will be using.
You can also add these resources as costs for units and stuff like you do with vespene/minerals. Its possible to create resource nodes for them by making copies of Vespene Geysers/Mineral Deposits and changing the field Resource Type to your 3rd/4th resource. I imagine you can change the name/picture for the resources too by changing the ingame UI, but I haven't messed with that stuff yet.