The first resource we have for Flexboxes is the tried and true MDN Web Docs. Used at the beginning of the semester, MDN continues to prove its reliability. MDN discusses flexboxes in extreme detail, talking about the axes of the flexbox, start and ending lines, the flex container, multi-line containers, and many of the various properties associated with them.
The second site we will be talking about was actually already shown in lectur material. While there is heavy detail in the matter-of-fact way that MDN hands out instruction, it can be described as fairly minimal in terms of design. css-tricks on the other hand gives you not only a well written explanation, but also a very good looking design interface.
The third and final resource for Flexboxes we'll be discussing is W3schools. W3schools has a little less content than the other two websites, but the argument for using them over the other two, is that they are far more beginner friendly. The tutorials are less explanatory and are more straightforward and simple, giving you the example code and a visual. I'd recommend this resource for beginners and then lead them to the other resources later on.
In Summary, we talked about 3 different websites that provide helpful tutorials for learning how to use Flexboxes. MDN, which has a very lengthy tutorial and explanation for those taking a deep dive into the subject, css-tricks, which has the most thorough mix of both explanation and examples, and W3schools, which is the most beginner friend