1. Tap the wall in several areas until you hear a hollow sound.
2. Turn on the stud finder. Adjust the device to the deepest depth detection available. This will prevent it from detecting laths, which are shallower than studs.
3. Hold the stud finder flat and firm against the hollow wall surface. Holding it against a solid area prevents proper calibration. Wait for it to calibrate. It will beep and display "Ready" when it's ready to use.
4. Move the device horizontally over a small section of the wall. It will beep continuously when it detects a stud.
5. Lift the device, recalibrate it and pass it over the wall a few more times until you get consistent results. If the device beeps every time in the same place, you have probably found a stud.
6. Drill through the plaster with a masonry bit, and then continue drilling with a normal bit. If you continue feeling resistance, you have found a stud. If you stop feeling resistance, you have found a lath.
This steps will help you a lot when you look for a stud. After finding it, you can install the mount according to instructions. Normally there will be instructions in the TV wall mount you bought. If not, ask the seller to get one. Hope this will help you. If you still have questions, you can search more or contact me. I'll be glad to help you.