Trading with Players
To begin trading with another player, just left-click on him or her while being close. The other player will then get a request if he or she wants to trade with you.
If the trade request is accepted, you should see the following window:
Just drag items that you want to give in your area. You will also see the items your trade partner is willing to give into the trade. Remember that you can always examine items by right-clicking them. Additionally, you may give coins into the trade or demand the other player to do so. If both players check “Accept Trade”, the trade is finished. Both checkboxes are automatically unchecked if either one of the players changes something (e.g. adding or removing items, changing the coins given).
Trading with NPC Merchants
Again, just left-click on the merchant while being close to open the trade window.
Buy/Sell Items 
Left-clicking on an item in the NPC trade window will instantly purchase it, if you’ve got the coins. Sell items by dragging them into the trade window or by pressing Q. The sell value is usually 1/4 of the item value. Increase certain skills to increase the selling and decrease the buying price. The condition of an item also affects its value.
Buy Nails 
Every construction needs nails. So just buy as many as you want and can afford, as NPCs never run out of nails.
Trade Pixels 
At some point you’ll likely get into a situation, where you lack pixels of the color you really need, but might have a surplus of useless pixels. To counteract that problem, NPC merchants will trade your pixels – initially with a rate of 4:1. You can improve that ratio with certain skills.
Now that you’re rich, how about owning your own legitimate property? Continue with the chapters about construction.