Follow the steps below to create a trade.
Step 1.

Login to the site. (How to?)

Step 2.
Click the "New trade" button in the menu.

Step 3.
Choose an application from the list.
After that choose the items you want to trade.
The chosen items will be shown on the panel at the top.

Step 4.
Add a short message to your trade and click the "Post trade" button.

You will be redirected to the trade page if the trade was created.