For guitar, we use numbers in different ways. One primary way, is to indicate frets. We write numbers on lines to show which frets we play on which string. This is tablature.
A riff is a recognizable tune which can define a song. It is a memorable guitar “melody” which is singable.
Here’s a wildly popular and common starter riff.
For simplicity, we can use just the string/s that we need. We can indicate which string/s we want to use by using string indicators, such as [the one string] – on the left side of the line.
Try this guitar riff on other strings. Since all of the tones are on the same string, it will work on any of the other strings. We have to know how the tune goes, since rhythm is not indicated.
On the recording, this tune is played on the middle two strings [D and G – 4 and 3], at the same time. We can use 2 fingers to play it [1 & 2 or 2 & 3], or use a bar. If string 2 is picked up under the bar, this is okay!