For the logo there's several options:
- use text as your logo (wordmark) or shopname
- use PNG image file as custom logo, in 2 versions: 1 for regular screens, 1 for high-resolution screens (aka "retina")
- use SVG file as custom logo, with the option to upload a special more compact logo version for smaller devices
Logo as text: if you don't have your ow custom logo, you can show your logo or shopname as regular text.
PNG file types are pixel-based, so if you scale up this kind of image or view it on high-resolution (hi-res) screens, you won't get an optimized appreciation of your logo (pixelated, or blurred). That is way there's an option to upload 2 PNG logo files: 1 for regular, not hi-res screens, and 1 for hi-res or retina screens (like Apple is using).
SVG file types are resolution-independent vector image files, so there's no need to upload a retina version. But as an extra option we added the possibility to upload a special logo version for smaller devices, as a way to make use of a so-called "responsive" logo (with multiple logo versions depending on the screen size).