I would suggest to learn open chords (or barre chords if you already know them), and the chord formula:

C major - D minor - E minor - F major - G major - A minor - B diminished

I - ii - iii - IV - V - vi - vii*

The roman numerals fit the chords above... If you learn how to play these chords using barre chords, you can move the WHOLE progression up and down the fretboard to change keys...

Thing is, these chords all fit into a key, which means you can create your own chord progressions! Which mean, you can write songs!! You can also jam with anybody if they know the pentatonic scale or something

Start on a I chord, and pick any 3 other chords for example:

I - ii - IV - V
C major - D minor - F major - G major

play those chords using some sort of cool rhythm/strumming pattern you think up, and ... voila, you've got a verse of a song!

if you need me to clear up this whole concept, I will be glad. I didn't go into too much detail.