In case there are orders already in the order book that satisfy your price and quantity requirements, your order will be executed instantly at the available prices. Your order will never be executed at a worse price than you have specified, however, your order will be executed at a BETTER price, in case such an opportunity exists.
If you want to place an order and execute it immediately (market order), simply specify a low price (for sell orders) or a high price (for buy orders), your order will be executed at the best available price.
Make sure you have enough tokens/ETH in your EtherMium.com balance to place the order.
GO TO Main Menu and select Token Catalogue from the left sidebar. Find the token you wish to trade from the list or using the search box and click on it.
In the order box on the right enter the amount you want to trade as well as the price for which you are ready to make a trade. Press Buy or Sell depending on the direction of your trade.
Verify your order in the popup box and press CONFIRM ORDER. If you are using MetaMask, you will have to open MetaMask and press "Sign" in the message window.
Your order will appear in the order book. If you have set a price worse than the price available in the order book, your order will execute immediately.
You can see the status of your order in the ACTIVE ORDERS section, or in the ORDER HISTORY for executed orders. Your trades will appear in the MY TRADES section and History (from Main Menu).