There are literally millions of places to start with this. Manufacturing has a lot of fundamental ground everyone needs to cover, and I frankly haven't even touched on a lot of required subjects.
There are people out there who already have a lot of knowledge to help us get started in manufacturing. The problem is, most of them are too busy to actually share that knowledge. If they aren't actually too busy, odds are they don't have a good platform established to push their content out.
A friend who is getting involved in the manufacturing world himself showed me this. Titan is an American manufacturer who is releasing content weekly to help the public grow their knowledge of CNC work. Titan really loves America and American values, and wants to push to bring jobs back to the USA where they belong. His mission is to inform the public to make that happen.
I have been looking for some introductory knowledge to help me wrap my head around CNC work. I've been researching laser cutters, 3D printing (I even purchased a 3D printer a week ago, and love it) and other tools. These machines aren't cheap, and I don't want to have it sitting around in my garage for a year before I finally work up the courage to learn how to use it. Instead I wanted to learn as much as I could before needing to get hands-on with it and/or put forth the capital.
Please check out his website. There are a few tutorials up, but there are a lot of other videos which have valuable knowledge.