It is also the past participle of the verb to be. The equivalent of " been " . So it is used very often.

J'ai été : I have been

I probably wouldn't translate "J'ai été" as "I was"

J'ai été en Australie: I have been in Australia

J'étais en Australie: I was in Australia

J'ai été malade: I have been ill. 

J'étais malade: I was ill

J'ai été travailler: I have been working.

Something more, an other reason for which you will often see it is beacause there no simple past in french, so we only use the present perfect (at least in the usual language).

So every time you want to say either " I was " or " I have been ", you must say " J'ai été "

Uhmm... it's better to translate "J'ai été" as "I was".  "I have been" is a word-for-word translation, but the grammatical function of the two phrases is quite different.