Watch the tutorial here: https://www.youtube.com/watch?v=MVDsvbajxwY
Add a shape layer. For this example, use an ellipse.
Add a stroke and a trim path using the "add >" menu in the panel
You want to use a stroke, not a fill, because a fill just fills up the circle. Using a stroke will allow use to draw the circle.
Make the stroke thicker so you can see it.
Edit the start and end keyframes of the trim path.
If you want to go clockwise, in this case, your end should be 100% at the finish and 0% at the beginning. Your start would be the opposite.
If you match the stroke "size" to the ellipse "size" you will have a filled circle. Otherwise, there will be a blank circle in the middle. Remember you're dealing with a stroke.
Now, you can play your animation, and it will be a wonderfully animated circle being drawn.
Change color, duplicate, and resize as desired.
Simple as that.