The one thing that has always characterized Metroid has been its approach to power ups- they are hidden and tucked away around the world, and as you get more of them, you gain new abilities, letting you access more of the world (and therefore, more power ups in turn). It’s one of the most satisfying gameplay and structural loops in gaming- and it is enhanced, if not outright better than ever before, in Metroid: Samus Returns, too.
There are, of course, a lot of power ups and collectibles to find in Metroid: Samus Returns. A lot of these are optional (missile ammo expansions, and the like), but some of them can be essential. But no matter what the importance of a collectible is, if it is in this game, the video below shows you how to get it- all collectibles, needed for your 100% progression.
Just remember, however- there will be severe spoilers (at least location spoilers) in this video. So make sure you’re not jumping ahead of where you are in the game.