How can I input individual students

Input the individual students into timetable only for timetabling purposes and if your timetable is based on students choices. Otherwise it is not necessary and you can use the basic class - division - group approach.
Please see: How to input Options - each student needs to select one course from Options1 and one from Options2

Before adding students it is necessary to create the classes, because each student must be assigned to exactly one class.
Please see: Čo sú triedy (ročníky)?

Then you can input individual students in the main menu Students/Seminar - Add. The dialog with two options displays.

A. Add one student
If you choose the first option the new dialog Student appears.
Here you can specify - Students full name (Last name, First name), select the class/grade the student is assigned to (and you have created before), and optional information as E-mail or phone number. If you choose this first option, you can also directly specify all subjects (courses) this student has chosen:

B. Add more students
Second option displays the dialog, where you have to specify the "Class" first and then input the names of all students names assigned into this class (one line for one student). The order Last name/ First name is taken by this setting: Konfigurácia formátu mena (Krstné meno / Priezvisko)

Note
Inputting the students picks can be done for more students at once in other ways, so maybe this second option is more convenient and quicker.

C. Import
You can input students also via "Import" function.
See these two articles for more information:
Import students' course(seminar) selections from clipboard(Excel) - Method 1
Import žiakov pre semináre z MS Excelu

As a result you will see list of all your new students as they were added or imported. In case you need, you can sort the list according column by a simple click on header. In case you wish to sort the list by more columns, hold "shift" key on your keyboard and select second column (e.g first sort by class, then by name).