When you sign up on MoonTrade, you can buy and sell BTC, ETH or XRP. from any other user.
If you want to be a trader, i.e. post ads to buy and sell any of the above cryptocurrencies, then you need to go to:
"Settings" -> "Become A Vendor"
and voila! Now you can Post "Buy" and "Sell" ads.
You do not need to deposit any crypto in your wallet to start posting ads and to begin selling. In the future this may be revised to prevent spam. So, Sign up! You will be able to post ads as soon as you do.