Complex sentence: After "grundskola", many Swedes attend the elective "gymnasieskolan", upper secondary school, choosing either a university-preparatory program or a vocational program.
Split into simpler sentences: After "grundskola", many Swedes attend the elective "gymnasieskolan" which is High School ("Upper Secondary Education" internationally). At the Swedish High School the students choose either a university-preparatory program or a vocational program.