What is SVG?
SVG is a drawing rather than a grid of pixels: shapes, paths and text described in XML, so it stays sharp at any size. That makes it right for logos and icons and useless for photographs. Converting it to a raster format fixes the size it will ever be.
What is JPG?
JPEG is the format photographs live in. Its compression is lossy - it discards detail the eye is bad at noticing, and discards a little more every time the file is re-saved - which buys enormous size savings on photographic images and makes a mess of screenshots, logos and text. It has no transparency.