When I play a triplet I usually play the note below the regular note, then the regular note , then the note below it again,(e.g. DED or EFE etc) At the start I just played the regular note three times until I got the hang of it. Up and down strokes or down and up depending on what direction the note before the triplet is played. Thats how I do it and it works ut fine.

The thimble is just a piece of 3.4"plastic PVC piping, like the type used by plumbers. Cut a piece about 3/4" to 1" long and cut at an angle one edge, so that it looks somewhat like a mouthpiece for a clarinet , only smaller. It has to sanded with really fine emery paper #0000 to get a smooth finish, It is used much the same as a finger pick for a guitar except you have to hold the index finger with my thumb and 2nd finger just as I would hold a flat pick. There are few methods, you just have to experiment to find the one that suits you best. I don't really like the thimble, and find them a little too thick and prefer to use a flat pick instead. Hope this helps.