I have heard that electives involve something about doing optional courses. Please confirm exactly what they are, what extra costs they involve and whether they’re worth doing?
The exact definition of an elective changes from faculty to faculty, but as a general rule of thumb, an elective is a course that does not form part of the required courses for a particular degree. In general, electives are taken out of interest, for example if you wish to do an elective in Introduction to Philosophy despite it not being a required course for the completion of your degree.
Even though electives involve voluntarily choosing a particular course, in some degrees it is compulsory to do an elective as part of your degree. For example, many law degrees require students to take an elective, although there is a choice of electives that the student may take on. On the other hand, you may wish to take an elective merely out of choice - this is often done if students want to do a course in another faculty that is not related to their degree. For instance, you could be doing a Business Science degree in the Commerce faculty, but want to take on Psychology as an elective from the Humanities faculty.
In the case of a degree requiring you to take on an elective, there would be no extra costs; the cost of the elective would be included in your degree. If you voluntarily opt to do an elective, then it will implicate additional costs that would be equivalent to the cost of that course if it were part of your degree requirements. This cost changes from course to course.
In terms of whether it is worth it to do an elective (referring to cases where taking on an elective is voluntary), there are several reasons why you may want to do so, including improving your knowledge/skills/abilities and boosting your qualifications. Both would make you more marketable as a potential employee. However, obviously there are cost and time implications to taking on an additional course; this decision should not be taken lightly and will likely result in a decrease in your marks for other courses as you have to spread your working time over more courses. You will have to weigh up the benefits and costs for your particular situation and come to a decision yourself.