Hello BleeA,
The stargates can be a bit confusing at first, but once you try it a couple of times, it's pretty easy!
It appears that you are only clicking the sign once, therefore it is selecting the top destination which would be the "Tour" area, and the "Spawn" area when you're in the Tour area. To select a destination in which you may freely build and mine (without disturbing other players' areas), you have to click the sign multiple times to cycle through the destinations. There will be places named "Random 1" and "Random 2" and so on. These are the places that you wish to go to. Once you have one of those Randoms selected, you may press the button and proceed into the portal. Hope this helped. Good luck!