How to write method and execute from main thread ?

Example : Writing and calling method

def hello(text):
    print("Hello " + text)

# If statement below checks is from the main thread
if __name__ == "__main__":
    hello("world")

def defines a method hello with parameter names.
Method starts just after the colon :

If condition __name__ == "__main__" checks if the call is from main process.
If block also starts just after colon :
Next line is the call to hello method with some value.

When you run the program using python hello.py 
It gives result : Hello world