confused about strings

Hi, im getting a bit confused about what to do about strings, usually ive just used std::string for string manipulation , but im in the crossplatform international world now,
For this im guessing I should use _TCHAR, but do I need to always use this ie for internal file names? Or is it just used for text that could get displayed to the user
What do you do?
For this im guessing I should use _TCHAR, but do I need to always use this ie for internal file names? Or is it just used for text that could get displayed to the user
What do you do?