Draw a Shape layer circle. Set its stroke type to dashed. Apply a Trim Paths modifier and animate its Start ort End value to reveal the stroke. Create a matching circle below the dashes - duplicate the first, remove the dashes and change the stroke color. Alternate ways of getting this kind of effect would include text layers, where the text is tied to a circular mask path and has text animators for opacity to reveal it. Yet anotehr would be to use the good old Vegas effect on top of a Circle, then use a Radial Wipe. There's several more techniques, but for starters that should more than suffice. Just pick one that seems the most easy to you.
1. Select the Ellipse tool (nested among the shape tools quadrant in the tool bar).
2. Make sure Stroke is active and has the width you want, and Fill is turned off in the tool options (you can change stroke/fill options later if you want.
3. Make sure no layer is selected, and shift drag with the Ellipse tool. Also add the alt (win) or option (mac) key before you start dragging to make the circle grow from the center. Press the space bar if you want to relocate the circle on the fly as you draw it (without having to release the mouse button as you create the circle). The shape tools create vector Masks when a non-shape layer is selected, and they create shape groups in shape layers when no layer is selected or a shape layer is selected.
4. You will get a shape group called "Ellipse" inside a shape layer. Twirl open the shape layer and "Ellipse" shape group and find the "Stroke" property group inside the "Ellipse" group.
5. In the Stroke group, you'll find a section called "Dashes". Press the "+" (plus) button to add a dash. Press it again to add a gap. Set the dash length to 0. Set the gap to something like 10.
6. Still in the stroke group, set the "Line gap" menu to "Round gap" (Why are we doing all this? You're creating dashes with rounded caps, by setting the dash to a length of 0, you're making the two dash caps meet each other, with no visible dash in between, and form a circle for each dash. It's a famous Adobe Illustrator trick).
7. To reveal the circle line over time, add a "Trim Paths" path effect to the Ellipse group. Select the Ellipse group and use the Add menu inside the shape layer.
8. Animate the End property in Trim Paths with keyframes, so it goes from 0 to 100 in the time span you want.
For more information on Shape layers, shape tools, path effects, etc, see all the shape layer-related topics in the After Effects Help chapter on Drawing, painting and paths.