To ask and answer the question 'Who is your friend?' the process is quite simple.
Ko wai to hoa? (macron above the 'o' in 'to') - Who is your friend?
Ko Tim taku hoa - Tim is my firend
'to' (your) is replaced with 'taku' (my)
'hoa' is replaced with the name of the friend (in this case, 'Tim').