For basic image editing, Fhotoroom is a good choice in a thinly-stocked Windows Store. It features 15 editing tools, including such crowd favorites as crop, rotate, sharpen, flip and mirror. Fhotoroom also includes 21 photo styles and 22 picture frames and borders. The paid version costs only $1.50 and supports photos larger than 3 MP -- an important consideration with today's pixel-packed cameras -- and provides access to additional filters and tools.
If you'd rather use a traditional Windows desktop app with more editing tools, there are plenty of free options available, including GIMP and Photoscape, as well as Web-based alternatives such as Google's Pixlr Editor.