The good news is, you have loads of choice ! The bad news is, exactly the same ...
There are two versions of Python shipped with the Pi - 2.7.3 and 3.2.3 These are pretty similar, but do have some differences, so choice number 1 is: which version to choose to learn with ? Version 3 is newer, and will continue being developed, while version 2 is older, and so has a larger base of sample code available. I can't see myself writing code that depends upon external code that is only compatible with version 2, so I have opted to focus on 3. They are very similar in most respects anyway, so skills picked up learning one will transfer very quickly to the other version.
There is a package called Pygame, which adds functionality which is handy for games types of programs - moving shapes around the screen, checking for collisions, or key presses, that sort of thing. This is currently easy to set up for version 2, and rather more long-winded (and still really beta-stage software) for version 3. If you want as easy a start as possible, and want to do games stuff, then 2 might be better for you. Google will of course help you if you want Pygame for version 3. More hassle to set up, but once installed, it's there...
So, now you have decided which version you will be learning, you can choose a tutorial. There are many books which can be read free on the web, as well as a tutorial in the python documentation. More are available for 2 than 3, but good ones are available for both. It is impossible to make a recommendation specifically for you though. I suggest looking at a few, and seeing which 'feels' best for you. Some to look at are:
Dive in to Python (available for both 2
Invent your own computer games with Python (only 3
Learn Python the hard way (only 2
How to think like a computer scientist (both 2
In the end I opted for a variant of the last one available via this link
. It is not perfect for pi, as it has been tailored for a particular course, and assumes that you will be running the PyScripter IDE under windows. You won't. PyScripter is not available for Linux of any flavour. I use Geany instead (sudo apt-get install geany). This means that screenshots will not look identical, but there is no great problem there for me, so that is OK. You may prefer another choice.
The main advice would be to learn it by doing it. I use a browser in half the screen showing the book, and geany in the other half for me to program in. (Small side note here. On the pi, you can leave geany as the active window, but simply moving the mouse over the browser will enable you to use the wheel to scroll, without needing to keep clicking backwards and forwards. Nice.) Type lots of examples - even if they are trivial. You will make mistakes, and learn more from them than you would from just reading and thinking you have learned it. Do the exercises. Even if you know what the program will be. I have been coding (not Python) for donkey's years, and I am making silly mistakes in Python. Learning fast that way!
You will always get help from people here. The more specific the question, the better the help of course. If you want to know exactly how to set up geany, and use it to learn with, you can drop me a PM or post a question.
Good luck with whichever approach you decide. Look at the options, and pick what is best for you. Too many choices with no frame of reference to help you decide at this stage, but really, you can't make a wrong decision.