You can obtain a hero at "Summon" icon at the bottom of your Airship screen.

There are 3 ways of summoning a hero, which are Special Summon with Summon Stone, Normal Summon with Summon Ticket or Diamond,  and Type Summon with Spirit Stone.

In addition, you can obtain a hero with collecting sufficient number of Essences from monster hunting.

※ Your hero obtained can unlock a new skill through awakening.