Hi, Regina,
when you export, create a folder first, e.g. "my exports" on your Desktop, and export into this. You will notice, that HTML Export creates more than just file (the nature of HTML), e.g. a folder called "pictures" with pictures in it etc.
You need to upload the whole stuff without changing their relative position to each other. So if you have a file called "index.htm" and a folder "pictures" in your folder "my exports", then upload both (with all contents of the folder) to the same folder of your webserver.
Best
Matthias