I don't understand focal ratios like F7. Can some help me to rap my head around this?

Focal ratio is just the focal length of a lense compared to its diameter. Dividing the focal length by the diameter of a lens gives you the focal ratio. The higher the focal ratio the higher the magnification or power of a telescope, for the "same sized" telescope. A bigger aperture telescope will usually have a lower focal ratio than a telescope with a considerably smaller aperture, this doesn't mean that it would have less magnification. Like a 10 inch aperture scope may be an f 5 and a 6 inch aperture scope may be an f 7, the 10 inch scope still has a higher magnification than the 6 inch scope , because it has a bigger diameter, you'll have a lower focal ratio.