Snapping helps you perfectly position your sketches in relation to other sketches or the center of the transformation.
Midsnap and Intersection snap are implemented into our sketching engine. Select one of the endpoints of any line and simply drag it to another line, arc or circle. When you drag the point close enough, you'll see the other line, arc or circle getting highlighted (Intersection snap).
To find Midsnap (only on a line), just drag the point along the line and you will see/feel it will stick to one particular point, this will be your middle point. If snapping is still unclear, see how to use them in this video: