Making the cursor release the object so you draw another. Usually if you choose, say, a circle, it thinks you want to draw a cloud of random bubbles.
Putting a circle's centre where you think you are telling it, not at some random point TC decides.
Knowing what "snap" really means - which "snap", there are lots of them? - and how to know which one is apparently on when the displayed tools and tiny scrap of information in 'Help' suggests they are all turned off. I gave up when some unidentified "snap" mode locked everything including all snap switches, preventing any further changes to my poor little drawing.
So let's start with the basics. When you invoke a tool, it remains active until you invoke another tool, but it works with each click. There are a couple of exceptions to that, ignorable for now. There is no state in TC in which there is no tool active. You can invoke select, which doesn't affect anything itself, but which gives you access to editing methods applicable to the object selected, by hitting the space bar. That might be helpful if you've got a twitchy trigger finger. A standard centre-and-radius circle takes two clicks to place those features. If you're in a new drawing with no other objects, there are no features to snap to, so you
can place centre and radius arbitrarily. Even if you don't know how you're doing it, you
place them, TC doesn't arbitrarily decide. You can also tab + shift into the coordinates screen bottom right to place the centre, then tab into the data boxes, enter the radius or diameter, then enter to create it. Clicking anything after that will create another circle because the assumption is that you'll only be clicking because you want to do that. It draws circles at your
direction, they're not random bubbles unless your actions have been directing random bubbles. If you
want to do something else, you
click to invoke another tool.
TC is feature-based CAD. Snaps attach features to features. Circles, for example, have centres, circumferences and quadrants, so you can you can draw something else by basing it on those existing features, say bisect a circle with a line snapped across horizontal quadrants. Then the line has new features like vertexes at its ends, middle, divide points (you declare the number of divisions) and intersections with the circle you just bisected. Snaps are either permanently active ("running snaps"), or, with TC, inactive but so simple to invoke with hot keys that specify the snap feature you want to use. V for vertex, Q for quadrant, M for middle, S for no feature (where the cursor lies), I for intersection, C for centre. You can see where this is going.
As well as being used in creating objects, features are used in modifying/editing them.
Is this useful to you?