Advice on How to Subsitute/Replace a Text or Number

Hello All,

I'd like your advice on to use the functions substitute or replace in excel with few examples. Of course, I already went to the Excel Help base, but their examples didn't suffice me.
Basically, let's assume I want to replace a specific word in a cell which is comprised of two words, or comprised of only one word.
What functions would work best to do that and would this work on numbers as well?

Assume that:
A1: Paris France ---> How to you remove Paris in the 1st place and Secondly, How do you keep Paris and remove France.
---------And
A2: Paris France ---> How do you remove Paris and replace it by Monaco (keeping France),

Thank you guys, any link to this matter would be much appreciated