To combine two sections of a course, enroll the users from one section into the other section. If you have two sections of a course, you can enroll the students in section 2 in section 1. Any new students enrolling in section 2 will automatically be enrolled in section 1. You can make section 1 available to students and keep section 2 hidden. The same principle works with more than two courses. You can add as many additional sections as you want to Section 1.
To do this, enter your Section 1 course, go to the Gear Icon (top right of page) → More → Users tab → Enrollment Methods. Add a new enrollment method: Course meta link.
Enter the course number for Section 2 in the "Link Course" box (e.g. PHYS005) and click "Add method" to complete the process. Your Section 2 students will now automatically be synced into your section 1 course.
Keep section 2 unavailable to students and make section 1 available. Repeat for any additional sections you would like to add.
The enrollments are dynamic, so after the meta-link is created, any newly enrolled students in section 2 will automatically be added to section 1.
If you'd like to use the Groups feature in Moodle to keep track of students in different sections, you can automatically put all students from your Section 2 course in a specific group. This makes it easier if you want to email just Section 2 or want to keep assignments or forums separate by section. Use the "Add to group" function of the "Course meta link" settings to add this group. Note, you still need to manually add Section 1 students to a group (or email only students not in the Section 2 group).