The word estaba in Spanish means someone or something used to be somewhere. If you say, estaba yo na Zamboanga, it means I was or used to be in Zamboanga.
This is obviously where the Chabacano estaba came from. Estaba in Chabacano means 'to come from'. Here are some examples of how the Chabacano estaba is used.
Chabacano: Donde estaba ese comida?
English: Where did that food come from?
Chabacano: Estaba na mi tata este camisa.
Engish: This shirt came from my dad.
Chabacano: Con quien estaba ese regalo?
English: Who is that gift from?
In some instances though, the way we use the Chabacano estaba somehow looks like the way it used in Spanish. Here some examples.
Chabacano: Donde tu estaba?
English: Where were you? (or where did you go)
Chabacano: Estaba yo na banco.
English: I was at the bank. (or I went to the bank)
Chabacano: Estaba, nurse mi nana.
English: My nurse used to be a nurse.
Chabacano: Estaba, na San Roque mi nana ta queda.
English: My mom used to live in San Roque.
In the last two sentences, the word estaba is used to express that something happened a long time ago.