1. Log in.
2. Click on the Shop button on the Account Panel (the bar where you can see your rank, crystals, etc.).
1 — main page
2 — scroll down to see offers - Not all items can be purchased using tankoins, exceptions are bundles, premium account and tankoins themselves.
3 — choose an item
Click on the buy option
If you have enough funds and everything goes correctly, you should get a screen such as down below.
Having problems? Check Failed Payment Transaction?
Customer support service by UserEcho