In this type of puzzles a single loop has to be drawn through all squares of the diagram. The loop can cross itself: the numbers below and next to the puzzle indicate how many crossings there are in every row and column. We will solve a small instance of this puzzle as an example.
Let's first take a look at the corners of this little puzzle. We know that the loop passes through every square; it enters through a side and leaves through another. Because the corners only have two sides we know that we can draw line segments perpendicular to each of those sides.
In both the second and third column there is a crossing. Next to the puzzle we notice that those can only be on the third row, so we can draw them there. The loose ends that stick out at the bottom of the upper corners can only be connected by drawing them inwards. And to finish the puzzle without introducing any extra crossings, we connect the loose ends on top.