1. Click on the Messaging tile from the Home (Start) screen.
2. Next, you will see the messaging window. In the thread section you will see the messages headline with summary and on the right pane complete message is shown.
3. If you right click on a blank area of the screen, or simply tap Windows key + Z, additional commands are revealed. Those commands are Status (for settings your online status), Feedback, Delete (which will delete the currently-selected thread), Switch (for changing manually between supported services), and New, for starting a new thread. Other commands might be there. To add new contact, click on the New button and follow the wizard. That are the complete steps to use the Windows 8 messaging app.
Similar to other Metro style apps, Messaging also provides simple, full-screen interface which consists of threads pane for tracking the conversation you have with others and also a messages pane which contains conversations you had in the currently-selected thread, and even a text box for adding comments to that particular thread.