Why is it spelled like じしゅう and not just じゅう  or something?

Why is it spelled like じしゅう and not just じゅう or something?

Good question! It has to do with the kanji readings ^^ Every kanji has a specific reading -- or readings, in most cases. Using today's word as example, the kanji 自 is read (in this case) as じ. And 修 is read as しゅう. Put the two kanji together and you get todays word. As I mentioned earlier, kanji can have multiply readings; which can be a nightmare for japanese learners. But with practice it will become easier. I hope with helped. ^-^