If I do everything at once I will get confused, so I want to do it one by one.
If I do everything at once I will get confused. That's why I want to do it one at a time.
いっぺんにやると If I do everything at once
混乱する I get confused
から so/ that is why
一つずつやりたい I want to do it one by one/one at a time.
itには my work, my homeworkなど具体的な言葉を入れてもいいと思います。