SUDAH indicates that an action has been completed while BELUM denotes that it has not been completed or has not taken place. MASIH shows that an action has taken place but has not been completed.
SEDANG is only used to demonstrate that an action is/was progressing or is/was being carried on. Saya sedang makan. (I'm eating) Adik sedang belajar. (Brother is eating)
Maaf means sorry and it used when asking to be excused for imposing on someone or for something one has failed to do. It can also mean excuse me when used before requesting information.
Pak (from bapak -father ) is used by a child to address his father or an old man, a student to his male teacher, a sub-ordinate to his superior, etc. Similarly, bu (from ibu-mother) is used to address one's mother, lady teacher, or one's lady superior.
Ini buku saya. (This is my book). Ini buku anda. (This is your book). Ini buku dia. or Ini bukunya. (This is his book). It is important to remember the word order. The noun is preceded by the modifier.
BUKAN is used to negate a noun. Itu bukan meja.(That is not a table). TIDAK is used to negate a verb, adjective. Hidupnya tidak bahagia. (His life is not happy).