Originally Posted by: GuitarGeorgeKnowsIt doesn't show what strings to not play, like some tabs I've seen printed.[/quote]

You don't play the notes that aren't indicated. But, I think what you are getting at is that the tab or notation doesn't indicate which notes to mute.

Using Xs on the tab or notation indicates that you mute the string but still strike it, in order to make a ghost note (a rhythmic click with no pitch). But that's not the case for the vast majority of notes, simply because you don't play them.

[quote=GuitarGeorgeKnows]However, if some of these multi-note formations are chords, how do you know what strings not to hit (for example, if you are not supposed to hit the low E or high E, they never seem to be X'd out)? Am I supposed to assume every string that doesn't have a fret number gets played as an open string?

If a string has no note indicated, then you don't play it. Ideally you avoid striking it with your fingers or pick. Or you mute it so that if you inadvertently strike it, it makes no unwanted sound.

The general answer to your question is to mute all the strings that you don't want making sound.

Use your picking/strumming hand palm to mute any & all strings that you don't want to ring. Use your fretting hand to mute also. When you are done fretting a string don't pull your fingers away from the strings. Continue to make slight contact with the strings. Just release enough pressure to stop the string from ringing. Keep enough pressure on the strings to stop them from making unwanted sound.

Also, remember if you are a beginner, then you are doing great just to get some notes fretted, picked & sounding good! Muting is another layer of technique to add in once you get the basics mechanics of fretting notes. Guitar is a constant process of refinement. Your scale in that video sounds good for a beginner. You just need to add muting to clean up the unwanted sound!

I cover basic right & left hand technique involving muting in this series of lessons.

https://www.guitartricks.com/lesson.php?input=10657&s_id=359

This tutorial covers fretting & strumming hand muting. In particular have a look at the beginner level tips.

https://www.guitartricks.com/tutorial.php?input=2281

Hope this helps. Please ask more if necessary & best of success!