Cannot see media on “preview page”

I have been having this problem a couple of days and I dont know what I am doing wrong. After I add media to a page (and can see it in the editing window) and then I click on Preview Changes”, it comes up empty on our webpage. Also, sometimes when it does “autosave” the whole thing disappears and I have to refer to an older save and restore it… Where can I find instructions on how to add media effectively? I don’t know what is happening? How do I save changes and then have them update on our webpage each and every time I add a picture? Thank you! ??