[Tutor] Converter

[Jack Lucas]

I am trying to make a converter for Python on my Mac. I know I can find one online, but this is more satisfying.
I am not sure exactly where to start. I want to be able to input a "Unit to Convert" a "Unit to Convert to" and an "Amount of Unit to Convert"
For example Unit to Convert: centimeters,  Unit to Convert to: inches, Amount of Unit to Convert: 2.5. Thus you would get 2.5 Centimeters is equal to 1 inch. Or something like that to display. I have no idea where to start, as I want to be able to input any Unit to Convert (will keep it simple for now, feet, inches etc. and add more later.) and have it display the unit I want to convert to, and not all the other junk. Can anyone help me? Atleast get one setup, as I am sure I can then copy and paste, and make minor changes for the rest. Also if someone would not mind explaining WHY I do certain functions, as I am new to Python.
Thanks