You can only trade of you have something to trade or to buy.
But if you mean trading without exporting your own money from your own wallet, that is possible. Many people here gain more money from bounties, airdrops, and signature campaign than trading, except the value you trade is pretty high enough.
Yes bounty campaigns and airdrops are the better options for us to earn cryptos here that can be used for trading. Some people also cling to faucet sites and mining but this take time, bounties are much better. To be honest, it would be hard to start trading with zero capital because some exchanges require ethereum to be used as gas, even when sending altcoins from MEW needs gas also. To start in trading you might want to have bitcoin or ethereum first.