Read the the terms of the trade and make sure you can comply with them. Use this form to send in a trade request with the sum you wish to trade. After opening the trade request it is possible to discuss with the trader in LocalParticl.com messaging system.
Open trade requests and message inbox can be found under Dashboard under your user profile page. You can send and receive messages with the trader there.
For more information see quick buy guide.
You can cancel the trade before making the payment. You find open trades under Dashboard in your user profile.