To solve you need to draw a single line ("snake") joining the two marked cells (each end). The line may never touch itself, not even diagonally. The numbers outside the grid show how many cells contain a snake segment in the corresponding row or column.

Input tips
Select an icon to the right to make that the active value. Then click a cell or drag your mouse over multiple adjacent cells to set them in one go.

Snake segment
Clear segment (unknown value)
Cell known to be clear

Use the mouse scroll wheel up/down to quickly change the active value or enter "S" to set active value to Snake, or "D" for active value dot, or space for blank.