You only have to put your finger somewhere in between two frets to get a particular note, so you can play more than the tiny handful of chords that can be played on something like a violin.
There are non-fretted guitars but they are rare, and I think early banjos were not fretted.
I can play chords on a violin or viola and strum them. Keeping a four-finger chord perfectly in tune in rapid changes is really hard (near impossible) without frets.
There are those who say it isn't a chord until you have 3 notes. I'm going to skip the complex music theory behind the arguments (I haven't studied them enough to understand much less form an opinion).
Of course in most music contexts there is more than one instrument playing and so the others can fill in the missing note making a full chord. Only a "one-man-band" really feels the loss.
Every jazz player knows you can drop the fifth, and the root too if the bass is filling it in. That gives your fingers room to add even crazier extensions
If not, stop and watch it. But make a cup of tea to enjoy with it first, and maybe put a cloth over your keyboard for when you inevitably splutter tea all over it.
in college a good friend was a very good Oud player (plucked, some number of strings.... more than 8? I forget), and it definitely sounds different from guitar due to less sustain. Clearer notes and chords, but they don't linger as long or loud.