Playing an instrument by ear requires a well-trained ear. You should strive to gain perfect "relative pitch", because "absolute pitch" is not realistic for most

Playing an instrument by ear requires a well-trained ear. You should strive to gain perfect "relative pitch", because "absolute pitch" is not realistic for most people unless you acquire it at very young age. The free app, Functional Ear Trainer (iOS and Android), has been an immense help for me and people I know. Use it for 10 minutes a day and sing along with the notes. Soon you should be able to recognize and sing certain intervals with 100% confidence, regardless of the key. The most important intervals for songs in a major key are: Octave, Perfect 5th, Major 3rd, and Perfect 4th It helps to learn songs that you can associate with each interval (going up and going down). Just google "songs for each interval" and find songs that work for you. Training your ear is the first step. Then learn how to reliably find each of those intervals on your instrument.