I can't complete the initial odyssey mission. I can't hack the door because I don't have enough energy. Where can I get energy? Why did the developers make a game that's so confusing for newbies? I don't understand what I should do in this game.
Welcome! There's a lot to learn in Elite, it's what keeps the game interesting.
Shields use a lot of power, maybe you turned yours on. The key is C for me. Otherwise, just walking around outside enough will drain power because your suit has to counteract the low temperature. There are places to power up - they look like lightning signs on the minimap - but if the settlement has no power you will need to get a battery. Part of that tutorial has you find a battery on the wall, it looks like this:
You can take one for later with E or use one right away with F. Not sure if I changed my keys but to use one later I press left-alt to bring up the actions wheel and move the mouse to the left: