Merhaba.

If I would like to ask a stranger for assistance how exactly would I say it? Let´s say I´m in Istanbul and I would like to ask for directions or something like that, would I ask:

Affedersiniz, bana yardımcı olabilir misiniz?

or

Pardon, bana yardımcı olabilir misiniz?

or

Özür dilerim, bana yardımcı olabilir misiniz?

In particular what´s the word that should be used at the beginning. Should it be "Affedersiniz", "Pardon", "Özür dilerim" or something else perhaps? It seems "Excuse me" has many meanings in Turkish.

Thanks in advance.

affedersiniz is correct, you can´t use pardon and özür dilerim in such situation.

Why not? I use all of them