Eighth note triplets are just groups of three notes that fit in the space of one quarter note. Counting them as tri-pl-et makes them easier to time and play. Here is a video if you want to learn from someone https://www.youtube.com/watch?v=wksS_klLRPo.
This is a Jeff Buckley-type version of Hallelujah, arranged for low G uke tuning. It only really sounds good on a ukulele with a low G string (the Aquila non-wound red low G strings are long-lived, sound good, and can be bought singly).