Mini Guide: Buying ARK using COSS.io

1. Visit coss.io and create an account, follow the steps to activate your account and login.
2. Once logged in we need to get to the wallet section. If on the exchange part, in the top right, click 'Account'. On the side menu click 'wallet'.
3. You can buy ARK on here using BTC or ETH. So, for these purposes I will explain using ETH.
4. Find ETH and click 'deposit'.
5. Send ETH to the address it gives you - wait a bit, there will be a spinning gear wheel beside the currency when the deposit is pending. I just refresh a bit.
6. Now that you have ETH, lets sell it for ARK. On the top menu select 'exchange'.
7. In the search bar type 'ARK' and click ARK/ETH.
8. Under the 'Buy Ark' header there are boxes, 'Amount', 'Price (ARK/ETH)'. Below those boxes there are selling orders. The top one is the person selling for the cheapest. Let's assume we want ARK right away and don't want to wait. Under the selling orders menu, click the top rows price value
9. Adjust the amount of ARK you want to buy by changing the value in the amount box manually. Note that the seller might not have enough ARK for you to buy, in this case you click the next line's price value and buy more ARK.
10. If the order goes through it will tell you and it will show up in your wallet. If not, the trade sits open. You can cancel it any time by hitting cancel, found at the bottom of the page under 'my open orders'.
11. Buy some COSS while you're at it. It's similar to BNB and the market cap is peanuts. 

Source (all credit due): https://www.reddit.com/r/ArkEcosystem/comments/75r973/mini_guide_buying_ark_on_cossio/