Pourtant could be translated by "quite" but it's not that simple. It implies that one thing happened when another thing was expected. It also saves you from having to spell things out. The text in braket is not part of the translation. It's the thought that is implied but left unsaid. J'étais pourtant sûre d'avoir pris mon porte-monnaie - I was quite sure I brought my wallet (yet I can't find it) Il semblait pourtant si gentil ! He seem quite nice (however he turned out to be quite the opposit) Cuisiner est pourtant si simple ! Cooking is really easy (yet you seem to struggle with it)

Yes,it has some different meanings. such as :but, however, nevertheless, yet. Sorry, my french is not well so I could not give some example sentences to you.