I’m confused by the references to resolution and file size. How do I know what’s right for me?
300dpi images will generally give you print-quality results. 72dpi images are more appropriate for web-use. JPG images are considered to be in a “compressed” format, and generally come in at about one tenth the size of an “uncompressed” file. If you see a reference to a file being “40MB uncompressed”, chances are it is only 4MB as a JPG, and thus will not take long to download.