The game is pretty simple, to control red press "F" while holding the red block and press "F" while holding the blue block to control blue. In this game you cannot jump, so you'll have to figure out how to get on top of the emerald block(s) using both red and blue's combined efforts. Never A Challenge Too Hard is a co-op style minecraft map for singleplayer use only, this means it plays similar to the generic co-op style map but you shouldn't attempt to play it with more than one person as it will break the gameplay.
If you do encounter an error in one of the levels, or simply want to return to the lobby: Save & Quit from the world and reopen it. By doing this, the levels will reset but your progress will be saved.
To reset all progress along with the map in it's entirety, (use this if you kill red or blue) there's a reset button for you to press at the far end of the lobby- combine pressing this with the save and quit tactic mentioned earlier and you'll be good to go.
Basically everything you need to know the map explains- so just make sure you're in 1.15.2 and playing alone. Enjoy! :D