Reddit reviews Machining Fundamentals

Start with https://www.amazon.com/dp/1619602091/ to get an idea of what this wacky world of machining is about. Your local library may have a copy.
On the endmill specifics, you'll need the tool diameter, number of flutes, and the chip load (usually in inches per tooth). If you don't have data for your specific tool then look up specs for other tools with the same diameter, number of flutes, and composition (high-speed steel or carbide are most likely). Here's a good overview of calculating speeds and feeds: https://youtu.be/ip2jm_6aUyk