That video is good, but it doesn't fully explain it.
Basically all you are doing is mixing the aileron channel with the elevator channel. Because servo 1 is in the aileron and servo 2 is in the elevator, and you want the two servos to work together, you must mix those two channels together so a movement on one channel will effect both servos. Note that you may end up having to switch the two servos with each other. With the Hobby King Tx, this requires using two of the three mixes. You want CH1 mixed into CH2 and CH2 mixed into CH1. (Depending on which channels are set up for aileron and elevator.) You want those mixed at 100% because you want full movement. One channel fully moves the other. I don't think the end points matter as the video claims. Sometimes you have to reverse a channel or two to get the mix to work correctly, and sometimes you even have to switch the two servos (where they are plugged into the Rx).
Some Txs have a Delta mix programmed into them already and you just select it. Always make sure it's working properly before you fly. Test the elevons just like in that video xuzme720 posted.