Equipping Jutsus
Your active loadout holds up to 4 learned jutsus. Open /jutsu info, select a learned technique, then use Equip or Unequip. If all four slots are full, Kakashi asks you to replace one of the techniques already prepared.
Learning and equipping are separate states. A newly learned jutsu is auto-equipped when a slot is free; when the loadout is already full, it stays in your collection until you choose a replacement.
Loadout choices matter in battle because the prepared techniques are the ones surfaced as your normal jutsu actions. Rank alone is a poor way to choose: compare chakra cost, nature, role, mastery, and your build. A cheaper mastered technique can be more useful than an expensive high-rank option you can only cast once.