If your Ethereum wallet is not connected to a stock exchange, ie over the MEW or MetaMask, you can not trade directly from here. First of all, you need to know where the token you want to trade is listed. If no specific stock market is listed, you can look at Ethereum token markets such as Etherdelta or IDEX. Usually the tokens from the airdrops do not make much money in the first stage. It is necessary to send the buyer you want to trade either to the stock market it trades with or to one of these markets. If the money you receive in this transfer is more than the value of token, there is no need to send it in vain.
In addition with that,
- after downloading some exchange like binance or bittrex (search for the erc20 tokens if it is listed on an exchange, if not follow what clonely's advice)
-it it is listed in any exchange, you have to send some eth for MyEtherWallet for you to be able to pay the gas/miners fee
-go to exchange (like binance search for erc token you have and copy address )
-go to MEW, click send eth&other tokens. Input to: (copied address from binance)
-input the amount
-generate transaction
-send transaction then wait for tx status
-after transaction status was confirmed, check your exchange (binance), check your funds if your token was already sent to your exchange.
-start trading by simple sell your tokens and buy another coins.
Hope it somehow helps you.
Goodluck!