The basic string documentation is at Built-in Types — Python 3.x documentation which a very good place to start. There is also Formatting Strings with Python which gives a great summary of what you can do with string formatting.
All the following resolve to being "True":"Geoff" in "This is how Geoff Does Stuff""geoff" in "This is how Geoff Does Stuff".lower()"dave" not in "This is how Geoff Does Stuff".lower()"This is how Geoff Does Stuff".find("Geoff")
However the last option is sightly different in that it returns -1 if the string to find is not found.
This is a simple way to update parts of a string:"Hello Geoff how are you?".replace("Geoff", "Dave")