Tuning

String instruments need to be tuned regularly. Whenever it sounds wrong, it needs to be tuned, which might be about once a week.

I recommend Fender's web app or iPhone app. There are many other very similar free apps.

Chords

To look up chords for songs, my go-to site is Ultimate Guitar.

Tabs

In class, students learn to play melodies from tabs. Here is a YouTube playlist of song they can practice.