Totems are statues that you can meet during temporary adventures.
You can get some valuable gifts from totems, but you will have to give them some rare items in return (which you can receive for completing Franco's orders on the pier or for sending airships in the main camp).
To make an offering, tap on the totem and, if you have all the rare items available, tap on the "Place" button.
If you don't have enough rare items, you may offer some gems to the totem.