Iv'e just purchased a Epiphone sg special 2 and a fender mustang 1 v2 amp. The problem I've got is when I connected it all up I fretted a string it played a note as if the strings were live. When I let the string go it sounded again. Is it the guitar or amp or just amp settings.
With an electric guiatr hooked up to an amp with medium to high gain, fretting a string (otherwise known as hammering-on) will make the note sound, almost exactly as if you had picked or plucked that string.
The same happens when you remove your finger (pulling off)
This is generally considered a very good thing in playing electric guitar, as it allows smooth legato runs, faster notes and runs and even allows you to play a melody line using hammer ons and pull offs while picking a bass line, for example.
If you don't like it, you need to back off the gain, and perhaps learn to damp the unneeded strings.
If you press a string down gently, more than likely, unless the amp and guitar are extremely loud, it won't happen. Likewise, taking that finger off, gently, will stop the sound of the open string. Unless the fingers are sticky!
It's hammer-on for the first effect, and if you do want the string to sound again as you pull your fretting finger slightly to one side, it's pull-off. Both very good techniques that guitarists use all of the time.