I would click on Guides to the left, and check out either Mazimov's All bosses or Yogi's 2 boss tutorial (they're the same category--All Bosses). It's a great jumping in point for Metroid to start learning!
Both guides mentioned will help out greatly for starting and I would also recommend joining the Discord if you haven't already. There are quite a few active runners there who post daily that love to help out anyone looking to learn. Good luck and welcome!
Is there any guide to mother brain? I can do everything else but the room to mother brain I cant get.
Mother brain room is the hardest room in the game to learn. I imagine both tutorials go through it but I'm on my phone and can't check.
If you have specific questions about it, I'd join the discord and ask there. Discord link should be on the menu to the left. There are many many active runners in there who can help :)