Guitar and Ukulele
The first thing you need to do is tune your instrument. I recommend the Fender Tune app for guitar or ukulele. It is free and easy for beginners to use.
You can also check the links below.
Tuning a Guitar
Listen to each string. Turn the knob until your string sounds the same.
Justin Guitar - Ukulele
This has free beginner ukulele lessons. This teaches chords and strum patterns.