If you understand guitar scales, you'll understand the foundation of playing music on the guitar. You'll be able to make up your own riffs, and create amazing solos just like professional guitarists.
Before learning about guitar scales though, make sure you're familiar with the notes on the guitar.
The major scale is your starting point should be the first scale you learn.
It is THE basis of chords and other types of scales, and actually the basis of Western music as we know it. If you learn the major scale, you will be able to understand how chords are constructed, know why your favorite songs sound the way they do, play great arpeggios, and be able to write your own songs.