Imagine you go on holiday. How would you present yourself to a foreigner?
What you wrote is fine. There is nothing wrong with the wording. However, if you wanted to improve it then -
Excuse me, I am French, could you please help me? Could you show me how to get to the post office?
Again, this is merely an option. What you wrote is fine.
Excuse me please, I am French. Can you please help me? Where is the Post Office?
Very good! Remember to use capitals.
Excuse me please, I am french, can you please help me find the post office ?