As soon as one of your Heroes reaches level 40, you can equip that hero with a random Talisman that gives their stats an additional boost.
Click on a Talisman to either Convert it or Upgrade it.
NOTE: A new talisman is selected randomly, so you may need to spend additional resources until you get the perks you look for.
NOTE: If you wish to level up a Talisman but keep its quality and effects, tick Save parameters. This option will additionally require Gems.