After seeing some of the idiotic things people do with a microscope, I can't be surprised, anymore. Here are some pointers, in no particular order:
1. The eyepieces can be adjusted wider apart or closer together. Humans have a range of interpupillary distance. We are not all the same.
2. When the eyepieces have the correct spacing between them, you will see a single circle. Not two circles.
The microscope is focused by moving the entire head up/down. Unless you change the lens or add lenses (barlow, for instance), the focal distance between lens and object were/when the image is in focus will be static. You do not turn the eyepieces to focus the scope (although initially you might have to adjust them to get the image focused in both eyes, plus you have to adjust them to where the microscope is parfocal if it is a zoom microscope).
Harbropoda's tip is important. I wear glasses, and I have to remove the rubber cup from the eye pieces, altogether. But I can still see an image with the cups on there. It's just a smaller circle with more black around the edges.
Some people can't use a binocular microscope, because they can't correlate the two images unless they are perfectly aligned. Some people can't use a binocular microscope because they are idiots. They might eventually get the hang of it if they used it regularly, but they otherwise can't get one to work without help. I've seen lenses turned upside down, eyepieces completely out of focus with each other, people who couldn't figure out the width between eye pieces is adjustable. All kinds of stupidity. Leave a microscope in given work place and it might get "adjusted" farther and farther away from usability until people complain the microscope doesn't work, anymore, and my naked eyes work better.
If you're experiencing a problem, first off, look thru only one at a time. Don't use both eyes until you get a proper image in one of them.