Picross, also known as nonograms, griddlers or japanese crosswords, is a rectangular grid where you need to find the encrypted image. Numbers in the left and top - it's blocks of the same color in a row or column.
Numbers 0-9 on the keyboard - color selection
CTRL+Z - undo
CTRL+SHIFT+Z - redo
CTRL+S - save
Central scroll - scaling or moving the field. With CTRL/SHIFT - scroll vertically/horizontally
Left mouse button, touch - draw with the selected color (CTRL / SHIFT will change drawing mode)
Right mouse keyboard - crosses to mark found empty cells