Creating concentric circles

Create two new layers.

Select the first layer, then from the little arrow button on the paths tab, select "New Path"

Select the Ellipse Tool

left click and drag where you want your center and once it appears, hold down the SHIFT and ALT keys to constrain it to a circle that’s centered on your initial start point.

Once you have it you your required size, select the foreground colour you require, right-click on the path in your list and select "Fill ", then select “Foreground color” from the drop-down list.

Switch back to your layers and select layer 2, and then back to paths. The next stage you can do either by copying your original path or the original (if you don't need it).

Ensure you have the path selected in the list, hover your cursor over it, right-click & select “Transform Selection”, which brings up a frame around the path. Holding down the shift and alt keys you can enlarge or shrink your path to suit by clicking & dragging one of the corner tags.

Select your second foreground colour and once again right-click and choose fill. You should now have two layers of different sized circle on the same center point.