3D printed mold techniques for long and short term usage
Yes, this is very broad. That said...

For high detail you want SLA. i.e. jewelry. If you just want a prototype of a mold, you can do a standard FDM style printer (95% of printers are FDM, and that number is a guess)

Really, you should be asking what material you need for your mold, but you can open a second question for that.

Do more research on injection molding. There is a great deal of information on how molds are made, i.e. How It's Made Plastic injection molds.

You will see there is a vast difference between a plastic, or silicon, mold and an injection molding machine. You are thinking that injection molding as a single mold, when it is really it is a system composing of several pieces of heavy duty machinery that can pump out hundreds of items a day automatically. However, it usually starts at 20k USD for the tooling for injection molding. Your costs could be a fraction of that or could be several times that. This is just a generality. So, if you are making 100 units you won't want to go down that route. For 10,000 units, on the other hand, it would be acceptable.