Aku is used for a subject on a sentence Ex : I want to buy a book tonight = aku ingin membeli sebuah buku malam ini Ku is used for genetive pattern Ex : my mother is sitting on the chair = ibuku sedang duduk di kursi Ku is also used for for a subject which is followed by a word with suffix "kan" Ex : I let her go = Ku biarkan dia pergi But you can also use aku (aku biarakn dia pergi)

both aku and ku-/ku- are pronouns. "aku" is written separately with the word that follows it. for example: aku mengerti (I understand), ibu aku (my mom)."ku-" or "-ku" is written as a series of the word that follows it or as a series of the word followed by it, in other words u have to connect it with other word. for example: kumengerti bahwa.. (I understand that..), setahuku (as I know), ibuku (my mom). I hope u can understand that :)