This really depends on what you known already, and on what needs you have as a learner.
If you are already programming in some other language, the "official" tutorial at python.org is a great place to start.
That's actually part of the "real truly-fine manual" at:
You might see some other definitions of RTFM online and elsewhere, with coarser language, but the spirit is the really the same. The ultimate source of information for a developer is in "the docs" for whatever programming language, OS, library, API, etc. you are using.
If you're not a programmer but are interested, willing and able to become one, then I don't think it matters much where you start. Every beginner's book, video course or website I've seen has things you'll need to "unlearn" later. What does matter is, does it get you interested enough to start writing code on your own? That depends more on you than it does on the source.
You can get information online, for free, but learning happens between your ears when you are writing programs, figuring out what series of steps will get a computer to do what you want, and then figuring out what went wrong when the results are not what you expected.
Take a look at codecademy.com or tutorialspoint.com as examples of web tutorial sites. Both provide online coding, so you can work from a mobile device, if needed. The sooner you get Python installed on a real computer and learn how to code that runs outside a website's sandbox, the better. You'll need a Windows/OSX/Linux desktop or notebook for this. Android, iOS, ChromeOS, etc. are designed for users, not developers.
After you can write simple programs without help, you might want to go back to the python.org tutorial and see what other things might not have been mentioned. Also, at that point, published books are a good (non-free) way to get well-edited information. I like Wesley Chun's "Core Python Programming" and/or Magnus Lie Hetland's "Beginning Python, from Novice to Professional" (it was titled "Practical Python" when I read it) both good.
And, if you want a good idea about what Computer Science is about, the free CS 101 video course at udacity.com is pretty good, assumes no prior programming experience, and uses Python as the programming language.