I get the premise of this and I think I’m just hung up on how to start. Start by writing def, the keyword indicating that you're defining a function. Stop trying to do programming homework in your head. Get on the page and think about it there, in code instead of in your mind. You're meant to write the language, not think about it. More on reddit.com

The first thing to do if your code doesn't work is to check the error log. Using your code without the function, the error is TypeError: unsupported operand type(s) for +: 'float' and 'str' What this means is actually pretty simple. The '+' operator does not work for a float and a string. This means that int(input()) * 1.6 + 'km' doesn't work as you are trying to do float + string. A way to fix this is to convert the float into a string using str(), in this case str(int(input()) * 1.6) + 'km' More on reddit.com

Think back to math when you had functions such as f(x) = 2x + 1. In a problem like this, you could substitute any value for x, and then you would plug it into the right side of the equation where ever an x appears. So if we wanted x to equal 3, our equation would look like f(3) = 2*3 + 1 , which equals 7. Similarly, we could write this exact same function in python like this... def f(x): y = 2*x + 1 return y If you were to copy this code into python, this is what each line would do. You would define a function called f, which can use an x value as a variable inside of it. This says what you want to do when you run the function. In this case, you're making a variable y equal to 2 times whatever x is plus 1. To make your function have a value, you type in return and then whatever you want the function to be equal to. In this case, you're making the function equal to y. So now that the function is created, you can use it whenever you want. For example, if you wanted to know what happens when x is equal to 3, you could type in f(3), which would plug in 3 for x and then return the y value for the equation you made (which is 7). Now functions don't only have to be for crunching numbers. You can also use them as a way to repeat code without having to do it over and over. For instance, let's say for some reason you need your program to print out "What time is it?" and "Adventure time!" multiple times while the program is running. Instead of retyping these two lines every time you need them in the code, you can make a function like this. def what_time(): print("What time is it?") print("Adventure time!") In this example, this is what's happening line by line. This defines a function called what_time. Since the parenthesis are empty, this function will be doing the same thing every time it is run. This will print out "What time is it" when the function is run. This will print out "Adventure time!" right after the second line is run. As you can see, there is no return at the bottom of this function, which means the function does not have a value. Instead, whenever you type in what_time() , it will just print out those two lines. More on reddit.com

Googled this: https://www.geeksforgeeks.org/understanding-the-execution-of-python-program/ More on reddit.com