German has a formal YOU (Sie) and an informal YOU (du). The formal YOU is used to address anyone you don't know, who is older than you, or higher in hierarchy, whereas the informal YOU is used with family and friends as well as people with whom you've sort of come to an agreement that using the informal YOU is fine. However, there needs to be a mutual agreement on this, otherwise using the informal YOU would be very impolite. So depending on who you are asking for help, you would say:
Können Sie mir bitte helfen. (formal YOU)
Kannst du mir bitte helfen. (informal YOU)
