Object Snap is a function which allows you to draw accurately in a very short time. This function employs some object snaps which basically are like magnets that make the drawn objects interact with each other “snapping” onto a specific object location when you are picking a point. For example, you can accurately pick the end point of a line or the center of a circle
To use this function you just have to select from the Tools menu the voice Object Snap. There you can choose between different interaction points, as you may see in the picture below.
To learn more about this important function, mostly about its practical use, see the video you will find here