Directing to def functions using if statements

So, hello guys. I wanted to ask when I want to use if statements to direct the user to the specific function to run. How is that being coded? For example I have 3 different functions like a,b, and c. And after asking the user about his input, and if he types 3 let's say, the python is going to pass the 1, and 2, and go directly to the function 3, and just run it? I really hope you are gonna help me, thank You so much for the time!