First, do you have that satellite plugged into the 3.3v port? If not and you have it in a 5v port, plug it into 3.3 or you will destroy it by over volting it. It looks like it is in a 5v port, but I can't tell for sure.
Second, UART3 and UART6 are just like USB ports on your computer. They just have different different port numbers. Both will do the same thing, but you have to be on the correct one. The gray wire of the satellite rx will be plugged into either rx3 or rx6, the 3 and 6 correspond to the UART port number. Which ever UART you are on, make sure you enable Serial Rx on that line. Then, go into the receiver tab and on the left hand side mid way (at least it used to be, been a while since I played with these) you will see a selection for Spektrum 1024, Spektrum 2048 and so on. You want the 2048 no matter what the satellite receiver is. I have never gotten them to work on 1024.
Once you are done with that, go back into the config tab and make sure Serial Rx is still turned on. Sometimes it turns off. This should allow you to see control movements in the receiver tab (I think). You will have multiple choices in here as well and if I can remember right, you just need to select Spektrum from the pull down. Hope this helps.