What the Pyraminx is
The Pyraminx is a tetrahedron, a four-sided pyramid. It has four corners, each made of a small tip and a larger layer underneath, and it can reach 933,120 positions not counting the tips (75,582,720 with them). Turns are a third of a full rotation, so there are no half turns.
Reading a Pyraminx scramble
Capital letters U, L, R and B each name a corner: U is the top, L the left, R the right and B the back. The move turns that corner with the layer beneath it, clockwise as you look at the corner. Lowercase letters turn only the tip.
The tips come last in the scramble because a tip turns on its own without disturbing anything else. Hold the puzzle the same way for every scramble so the preview and your puzzle agree.
How the scramble is generated
cubing.js picks a random position of the whole puzzle and finds a short sequence to reach it, then turns each tip to a random position. Random-state is what the WCA uses for the Pyraminx too.
Practising the Pyraminx
Pyraminx solves are short, often only a few seconds for experienced solvers, so inspection is where much of the solve is decided. Use the timer's 15-second inspection and try to plan your first layer before you start.