How to specify between two functions that are a part of a larger function.

I have two functions I want to put together in a grand function where I can specify which of the two functions to run in my actual input when I run my function. This could be via =True/False or the inclusion of a word (F1 or F2) or something like that. I am not sure how to go about specifying between the two sub functions in my grand one. An if than function, or some kind of call for which to use