How do we get vegetables?

In my environmental science class we learned about development of the flower or plants. I remember learning in middle school that there are many vegetables, including broccoli created from artificially selecting a certain trait of the wild mustard.

According to this, the suppression of flower development led to broccoli, suppression of intermode length led to cabbages, enlargement of leaves led to kale, sterility of flowers led to cauliflower, and enhancement of lateral meristems led to kohlrabi. What I wondered was, how did they do this. I also wondered, how did they think of forming these kinds of weird vegetables from such a normal plant. Finally, I wondered how long did it take to turn wild mustard into these vegetables.

I might do further research about this in the future, as it made me curious how our everyday vegetables are mostly artificially selected. I could use the Internet once again, or find related books about this. 

https://www.sciencealert.com/fruits-vegetables-looked-before-domestication