Numbered wide moves
From the 6×6 up, a wide turn can move more than two layers, so the notation adds a number in front. 3Rw turns the right three layers together; Rw on its own still means two. The ' and 2 work as usual, so 3Fw2 is a half turn of the front three layers.
How the 6×6 scramble is generated
Like every cube from the 5×5 up, the 6×6 is scrambled with random moves rather than from a random position, the same approach the WCA takes. 80 moves keep the many centre pieces and edge groups properly mixed.
Mean of 3, not average of 5
Because solves are long, the 6×6 is competed as a mean of three solves at WCA competitions, with no best or worst result dropped. When you practise, time three scrambles in a row and treat the mean as your result.
Applying an 80-move scramble
Like the 4×4, the 6×6 has no fixed centres, so start from a solved cube with white on top and green in front. Work through the scramble in short chunks, keeping a finger on your place, and check the preview at the end; it is much faster than discovering a mistake halfway through the solve.