Hi Yvonne
if an author of an LO has enabled resuming then when a learner navigates each page the url ends with a direct link to that page so that they can bookmark a link to when they last viewed the LO and resume from that point by following their link.
It also means that an author can send different links to different learners to specific pages within an LO.
It's also quite useful when actually authoring e.g. having the LO open on a particular page and then just refresh after making changes in the editor. Typically that is quicker than re-loading the whole LO each time via the play/preview buttons.
Finally with an LO exported as SCORM in most VLE's the learner would be able to resume where they last left off if the attempt hasn't been tracked as completed. But that may vary by VLE/LMS and configuration etc.
HTH
Ron