How did Dave get to Jade's planet if Jade didn't connect to Dave (cause one of the first portals leads to the server player's planets) and Dave didn't connect to Jade? Is one supposed to use the server player's portals to get to the other lands?

The first portal does lead to the player’s planet, the second to their server player planet, the third a different spot on the server player’s planet, the fourth goes to the server player’s server player’s planet, and so forth.  And Jade was Dave’s server player so he only had to go through his second gate to get to her planet.