The Priceless Maracas
This side quest will unlock for you the ability to expand your weapons, bows, and shields inventory to hold more gear. That way you don't have to keep on dropping something else to pick up something new. The maximum spaces you can have in each section is twenty and considering you only start out with five...that's a lot of room you could potentially have.
Hestu is standing despondently on the path that links Dueling Peaks Stable and Kakariko Village. Talk to him to trigger the sidequest.
Hestu will show you where a group of Blue Bokoblins took his maracas. It is behind a bunch of rocks. It will be difficult to sneak in, but whatever way you choose, you will need to defeat all of the Bokoblins before the treasure chest is unlocked.
Once they are all down, the treasure chest will unlock. Open it and you will acquire the key item Hestu's Maracas. Return them to him and...oh, they're empty. It looks like his fellow Korok Seeds decided to play a "prank" on him and have dispersed all over Hyrule, carrying the seeds that filled the maracas with them!
If you have at least one Korok Seed, Hestu will ask for it. Give it to him and you can choose whether to expand your Weapons, Shield, or Bow inventory by one space. Hestu will then need two Korok Seeds. If you have enough, hand them over and you will be given another expansion of your choice.
After this, Hestu will prepare to depart for Korok Forest and you will have completed this brief sidequest. Hestu will remain in Korok Forest for the rest of the game, ready to expand your inventory anytime. There are 900 total Korok Seeds in this game, but you will achieve maximum inventory size after giving Hestu 441 seeds. Time to start collecting!
Korok Seeds are scattered all over Hyrule. Each one has a very small, tiny puzzle associated with it. If you ever notice something "off", it's worth your while to poke around a bit and see if a Korok Seed is behind the mischief.