Hi. This is Hub Guitar.
I just got off the phone with my lawyer, who told me that unless I want the the chair sued out from under me, I'm going to have to use Twinkle Twinkle Little Star to teach you how to play melodies and other music by ear.
You're probably going to need to use your voice to do any of this work. You need a way to connect mentally to the music you're trying to play.
I'm hoping you can recall the melody to Twinkle Twinkle Little Star. Most people can.
First I'm going to sing the melody.
Now I'm going to find it on the guitar. In this case I know it fits in the C major scale because I sang it in the key of C major. If you try to do this with a random melody, you might need to determine the key first, which will help you figure out what scale to use to play it.
This process is simple. The key is to pick a tune that sounds easy. Then figure out what the key is, then play the scale associated with the key. From there you should be able to hum the notes to yourself and find them on the guitar. Take your time!