Draw a single non-intersecting loop in the grid that enters and exits each bold region exactly once. If a number clue is given in a region, that number indicates the exact number of cells used by the loop in the region. Unused cells cannot be orthogonally adjacent across different regions.
Grid control: To draw a line press the mouse button at a start cell and move mouse to another cell holding the button. You can also put auxiliary marks which don't affect submission by clicking at cells. More details about grid control are at the help page.