What are seminar/course lessons for?

Seminars/Courses are a special lessons dependent on individual student choices.

Expression "seminar" or "course" in this case means the group of students specified according their individual requests for the the same subject. So instead of groups from divisions, it is important to know every student's request for (elective) subjects and input them into the software alongside with students names.

Then the specific algorithm for individual students timetables checks collisions between lessons according to assignment of students to seminar lessons. This is different against ordinary lessons, where students are defined by using divisions/groups and it also means, that you have to input all your students into the timetable.

In most common cases when inputting the lessons it is enough to use just groups, like Boys/Girls or 1st group/2nd group... This way you will avoid needing to input all students into the program and assigning them to the seminar's lessons. Also in cases, when students make choices from predefined options (like art subjects, or language courses), which you wish to be taught always at the same time and not mixed (like "music + English advanced" even if students in these groups are different).
Please, see this: How to input Options - each student needs to select one course from Options1 and one from Options2

However, in some more complicated cases, you will need to input lessons as seminars (or courses). Especially for optional subjects, where students choose, which subjects they will attend from the list of available subjects without any other constraint. This kind of situation can be handled by groups if students pick just one subject from the list, but in case they can pick two or more, situation can be so complicated that you will need to use seminars.