I've heard of playing "tenths" on the piano. How do you play "tenths" on the guitar?
A tenth is just a fancy way of saying a third, used when the notes are an octave farther apart than normal. Try counting up from the root C to find the diatonic 10th: C-D-E-F-G-A-B-C-D-E. Notice that going from C to the high E is a distance of 10 (counting the first C as 1, since there's no such thing as a 0th). The tenth takes specific qualities like the third does, so a major 3rd an octave wider is a major 10th, and same with all other qualities.
A common use of 10ths is to create a more open-sounding harmony (and also to avoid the muddiness of low thirds); Try playing the F on your guitar's low E-string, and then play the A on the G string. Should sound nice, much less muddy than playing the same F with the open A string. Play around with it on guitar; you'll notice that you usually have to skip a string or two to reach them, due to the wide nature of the interval.
While they are often used to create the effect of an entire triad - since the 5th of a major or minor triad isn't super-important in determining the quality -, a tenth is an interval, not a chord. You could make the argument that they kind of are, since power chords are a thing, but at their heart they are intervals of two notes.
As an example, the little guitar part of Justin Bieber's recent(ish) pop song "Love Yourself" is entirely based on 10ths taking the place of regular triads.
How do you play tenths on guitar? Usually by playing two strings that have another two strings in between. Let's use G major as our key. Fret G on the bottom string, 3rd fret, and we'll need a B note a tenth above it. That lives on the third string, 4th fret. Probably best played with thumb and a finger, or two fingers. Possible by muting the in between strings, like Wes did with octaves.
If a tenth is played on 5th and 2nd strings, taking a G again (but an octave higher than before, as it happens), this time the G is on 5th string, 10th fret, and B is on 2nd string, 12th fret.
If we want to use 4th and top strings, a tenth is always two frets up from the root (just like 5th and 2nd string tenths).
Minor tenths work well too, but for those, the higher note is fretted one fret lower. Tenths sound good (although they can't be called chords) because particularly with notes in lower register played as thirds (say G with the next B note up from it) often sound muddy, mainly due to their harmonics getting mixed up with each other.
Thus they sound even better on bass guitars. Using bottom and top on a 4 string bass means the upper note is always one fret higher than the root. Try C/E sliding to F/A. Reminiscent of Lou Reed's Walk on the Wild Side?
They're not chords - tenths are intervals. It's an octave plus a third, and they're common in classical guitar pieces.
1A friend of mine, a piano teacher, was surprised when looking a score written for guitar; he once told me "it's amazing the length of the intervals you can play with only one hand on a guitar, I'd need both hands to play this"– BarrankaJun 9, 2019 at 10:59
@Barranka - they can be played with one hand - hammered on - but are better played using two - plucked...– TimJun 9, 2019 at 12:46
@Tim One fretting hand, then. Jun 9, 2019 at 22:23
If you mean tenth intervals, in addition to other answers, you might find this little (and easy) study useful: Julio Sagreras, Terceras lecciones de guitarra, 13 (p 23)