EVP stands for electronic voice phenomenon. An evp is defined as a recording of nonphysical and/or spiritual voices and/or noises that is picked up. Evp's are taken with a voice recorder. This can be a simple tape recorder to a digital voice recorder.
To listen to your evp's use a set of headphones and turn up the volume. Listen very close for the slightest sound. Instead of a voice you might pick up growling, singing, humming, or footsteps. You can use white noise. White noise is sometimes use in the background to help make the voices stand out, this can be radio static. You don't have to do this, it's your choice.
Most investigators breakdown epv's into different classes; A, B, C, and D. Class A is most clear to hear as if someone was standing next to you, with B being less clear and audible, C and D are even less clear and harder to hear like a whisper.
Thomas Edison, in the 1920's, made a few attempts to create a devise used for spirit contact, but he never succeeded. The first documented case was in 1959. Fredrich Jurgenson was in the Swedish countryside trying to record bird songs. When playing them back he discovered the sound of a man speaking Norwegian about songs of birds.