To make up riffs in the key of G learn the super simple solo pattern on the right.
The black dots show you which notes you can play.
The left of the diagram shows you which finger to use for each note. To play the notes along the top of the diagram you just play the string by itself (as an open string without any fingers on it).
At first, play the notes one at a time in the order shown.
So to play the first note, just pluck the low E string by itself.
To play the second note, place your middle finger on the 3rd fret of the low E string and pluck that string.
To play the third note, pluck the A string by itself.
To play the fourth note, place your index finger on the 2nd fret of the A string and pluck that string.
To play the rest of the notes just follow the diagram.
Then play the notes in the reverse order.
Once you get comfortable playing the notes in order, then you can skip around.