There are a few possible explanations for why students may be having trouble locating your course.
Under the "Edit course settings" screen from your course, you have the option to set "Course visibility." This option controls whether students can see your course. If you're currently using your course, you will want to make sure that "Course visibility" is set to "Show." If this option is set to "Hide," students will not be able to see your course, including students currently enrolled in your course.
After login, the courses that you're enrolled in are displayed in two places. They will appear in the lefthand sidebar under My Courses and also in your Moodle Dashboard.
The Dashboard can be accessed in the sidebar or beside the word "Moodle" along the top of your screen. A list of your courses will display under "My Courses" near the bottom of the sidebar content.
Your enrolled courses displayed under "My courses" in the sidebar, however, are only the active courses. Active means their start date has passed and their end date has not yet occurred. If you're finding that your course or courses are not showing in the sidebar, go to "Edit settings" from within your course and check the start date and end date that you have set for the course.