I have to work on urgent stuff so I can't go on with Flask for the moment. :( But I want to quickly pen down what I think might be the relatively easiest way to go from knowing nada to learning to make a web app, based on my experience.
Learn Python the Hard Way (LPTHW)
First half was good, second half got too hard, partly because the way things were explained did not agree with me. I quit this site in its last third, I think.
I think I did Python basics on this site in the same period I did LPTHW. I may have done one or two other basic tutorials too because I wanted strong enough fundamentals to make learning the harder stuff easier later.
I don't think my fundamentals are strong even now though. For instance, I've never written a class and I'm not sure I know how to.
Web Design for Everybody (Basics of Web Development and Coding), with Colleen van Lent
Lent is very clear on most things. I also did a Bootstrap course somewhere online but I can't remember what it was. Learning front end stuff helps me understand which code comes from what programming language and where it should go when doing Flask. Learning Flask will involve Python, SQL, HTML, CSS, and JS, at some point or other.
I didn't do the Capstone for this or any other Coursera course I did, because it costs money.
Python for Everybody, with Charles Severance
The first couple of Python courses in this specialisation are pretty all right. But I feel beginners require a lot more hands-on/embodied experience before we know to use Stack Overflow and other resources as vital supplements to understanding the things instructors miss out, and to troubleshoot all kinds of problems course instructors could not predict might affect their students. This is why it's a good idea to go through Code Academy and LPTHW before doing this Coursera specialisation.
Severance is the clearest instructor I've come across on the things he goes through in the "Using Python to Access Web Data" and "Using Databases with Python" courses. I gave up working on a couple of the more complicated projects towards the end, in part because the instructions grew less and less and I kind of still needed them. But most of the courses are really pretty damn great.
I didn't finish even midway through part 3 of this series but the first two parts gave me a pretty ok beginner grasp of Flask with respect to Jinja2.
For me, the clearest instructor and content so far when it comes to Flask. I'm slightly less than halfway through at the moment, though, I think.
UPDATE 19 April 2017: Model-View-Controller (MVC) Paradigm
At this point, I feel, it's time to focus on two things: security, and the MVC paradigm. I am presently trying to figure out flask-security, but haven't found good enough teaching/learning material for it. Please message me if you know some.
For MVC, this is a good introduction:
It helped me a lot, made me realise I could reduce my code by around 90%.
Throughout this journey, Stack Overflow has been absolutely vital for finding solutions to miscellaneous problems. But usually, I google my problems and it finds solutions on Quora and a lot of other great websites too. I tried duckduckgo but its results were dismal for research.
UPDATE 2 April 2017: Yes, CS350 is good, but slightly more than halfway through it, I found myself building my own web apps, and that meant that I began seeking solutions from everywhere. It was a sudden and significant decentralisation of sources. A bit more detail in Part 3 of my experience learning Flask.