You must have an ETH balance on your EtherDelta account before you can deposit tokens in their exchange. Here is the full explanation for it right from the EtherDelta representative who posted it on their subreddit:
Deposit
1. By now you should have an account selected in the account dropdown (upper right). Your account should be managed by either MetaMask, EtherDelta's browser wallet, or Parity.
2. In the account dropdown (upper right), next to your account address is your wallet balance. If it's 0, you need to send some ETH to your wallet address. Do that before proceeding to the next step.
3. Now that you have some ETH in your wallet, you need to deposit from your wallet to the EtherDelta smart contract so that you can start trading.
4. In the upper left, there is a Balance panel. There are three columns, "Token," "Wallet," and "EtherDelta." The first column, "Token," will have a row for the token you're looking at and a row for ETH. The "Wallet" column shows the balance held in the account you have selected in the account dropdown.
Notice that the balance shown in the ETH row under "Wallet" matches the balance shown in the account dropdown.
5. When you deposit, you will move funds from your "Wallet" to the EtherDelta exchange smart contract. To do this, enter the amount you want to deposit and press "Deposit." Don't deposit all of your ETH though. You need to leave some behind in your "Wallet" to cover gas fees. A good rule of thumb is to leave 0.05 ETH in your "Wallet" to cover gas fees for future transactions you will do (trading, depositing, withdrawing).
6. After you press the "Deposit" button, if you're using MetaMask you'll have a transaction to approve. You can reduce the gas price from the default (~21 gwei) to 4 gwei if you're willing to wait longer for your transaction to confirm but pay a lower fee. If you're not using MetaMask, you can set the gas price from the "Gas price" item in the account dropdown (upper right).
7. NOTE: If you are depositing a token (not ETH), depositing will involve two back-to-back transactions. The first one approves the EtherDelta smart contract to transfer the deposit on your behalf. The second one is the actual deposit. You must approve both.
8. After your transaction has been sent, EtherDelta will tell you that you generated a transaction. You can click the link to track your transaction on Etherscan.
9. Once your transaction confirms, you should see funds move from the "Wallet" column to the "EtherDelta" column.
Hope this helps.
