1. Dia datang
Dia datang means he came. Remember, verbs in Malay do not get conjugated when used to refer to any tenses. Dia datang can also mean he is coming.
Sebab essentially means reason, and it is a noun. However, in spoken Malay, this word is used as because. You might learn the word kerana if you are learning formal Malay.
Nak is shortened from hendak, meaning to want. This verb is more commonly used compared to its alternative mahu or mau.
The word bagitahu is actually a compound word. Bagi means to give (colloquial of beri). Tahu means to know. Thus, bagitahu means to tell or inform. The formal form of this word is beritahu.
Sesuatu is equivalent to something in English.