There is an editor guide that you can access through the help menu, but it doesn’t cover all features yet.

The startpos trigger is used so that you can start in the middle of a level while testing it, would be very tedious to replay the whole level each time you want to test out a new obstacle.

You will still need to complete the level without a startpos trigger to verify that it can be done before uploading it (practice mode is allowed).

Not sure what would cause that you die at the start each time. As a rule of thumb you should leave the first 10 squares or so of the level free. The character glides in from the left and if there is a block in the beginning he will collide and die right away :/

Let me know how beating the rest of the levels feels, hopefully it should start to feel more and more challenging =)