You can easily create concentric circles in PowerPoint by creating a circle, and then duplicating it several times. Then, reduce the size of some of the duplicated circles and align all them centered together (vertically and horizontally).
Instead of re-creating the concentric circles by hand and reinventing the wheel, you can use a concentric circles template for PowerPoint. In our catalog you can find thousands of concentric circle templates for PowerPoint and Google Slides.