Trade8 only accepts BTC deposits.
Make sure you've signed up to deposit.
To deposit BTC, go to the trading dashboard and click on the Deposit button in the sidebar to get a deposit address. Deposits are credited after 1 confirmation on the blockchain.
Trade8 also offers unlimited, risk-free demo trading. You get 10 BTC to demo trade, which you can refill indefinitely. Demo trading works exactly like real trading, except your balance is fictional. You can switch between your real and demo accounts from the top right corner menu of your dashboard.