What this suffix does
-let usually turns a noun into a smaller version of itself: drop becomes droplet, pig becomes piglet, book becomes booklet (a small book, a pamphlet).
But unlike -ly, this suffix is NOT productive. You can't take any English noun and add -let to invent a new diminutive. It only works with a small, fixed set of words that already exist this way.
The words worth learning
These DO feel like "a small version of something", the meaning still matches:
droplet = a tiny drop (drop = drop)
piglet = a baby pig (pig = pig)
islet = a tiny island (isle = island)
ringlet = a curl (ring = ring, a curl forms a ring shape)
booklet = a small book, a pamphlet (book = book)
These others come from the same formula historically, but the meaning has drifted so far that thinking of them as diminutives will not help you, just learn them as their own word:
bracelet = a piece of jewelry worn on the wrist (has nothing to do with "brace" in modern English)
tablet = a pill, or a device like an iPad (not "a small table")
leaflet = a flyer, a printed handout (not "a small leaf")
hamlet = a tiny village (you will not recognize "home" in there anymore)
And two that barely feel like diminutives anymore, they are just everyday words:
inlet = a narrow strip of water going into the land (or an opening where air/liquid enters a machine)
outlet = a plug socket, or a way to release something ("power outlet", "emotional outlet")
Two common traps
"Hamlet" with a capital H is the Shakespeare play character you might already know, but "hamlet" lowercase just means a tiny village. They are spelled the same but mean something completely different.
And "inlet"/"outlet" are NOT actually diminutives even though they end in -let: they come from in/out (entry/exit), not from a "small version" of anything. Do not try to memorize them as part of the "small thing" pattern, they are separate vocabulary.
A trick to remember it
Split them into two boxes: "STILL shrinks" box (droplet, piglet, islet, ringlet, booklet: the meaning still matches "small"). "MEANING CHANGED" box (bracelet, tablet, leaflet, hamlet: learn these as-is, don't look for logic). You only need to remember which box each word goes in, not 9 separate words.