What the Square-1 is
The Square-1 has a top and a bottom layer made of wedge- and kite-shaped pieces, and a middle that can split in two. Turning half the puzzle mixes pieces between layers, so it changes shape as well as colour. Solving it means restoring the cube shape first.
Reading (x, y) and /
Each pair in brackets turns the two layers: the first number is the top layer, the second the bottom, counted in 30° steps (one twelfth of a turn). Negative numbers turn the other way, and 0 means that layer doesn't move. A slash means: turn the right half of the puzzle 180°.
Start in cube shape and apply each pair, then the slash, in order. If a layer won't turn by the amount asked, a piece is out of place and an earlier step went wrong.
How the scramble is generated
cubing.js chooses a random Square-1 position, including a random shape, and works out the turns that reach it. The WCA scrambles the Square-1 with random-state scrambles too, which is why the puzzle almost never stays a cube.
Practising the Square-1
Because scrambles produce random shapes, getting back to a cube is part of every solve. Time full solves from real scrambles rather than from a shape you set up yourself, so your practice includes the shapes you would meet in a competition.