The core game of DCS is free to download and includes a couple of (not so great) aircraft to fly. You might want to check that out first.
There is a pack of fairly "simple" aircraft to fly, i.e. the Flaming Cliffs 3 pack, which has 7 aircraft included for a very good price. By simple, I mean that the controls are deliberately simplified. The flight model and visuals are all very good. That's the easiest way to get started and as the sale is currently running, pretty cheap.
After that, the rest is down to you, i.e.
- what era would you prefer to fly in, WW2, Korea, Vietnam, Cold war and would you prefer to fly a helicopter, warbird, early jet, the generation all singing and dancing
- the game includes a mission editor. Takes a while to get your head around it, but it's very powerful and allows you to build some very complex scenarios
- There are lots of online squadrons if you wish to fly with someone, varying between fairly chilled, to full on serious, focusing on just a few aircraft, full ATC etc
- the "full fidelity" aircraft allow full interaction with the buttons and various controls in the aircraft via mouse control whilst you're flying. Makes it MUCH more immersive, but they do cost more
Regarding learning to fly any of the aircraft, IMO the easy way is to do what a real pilot would do. ie. get and understanding of the aircraft by reading first, then practice take off, landing, radios etc, until you're proficient enough to work on weapons.
Be aware that DCS works best with a well specced PC, good HOTAS, pedals and in VR (again, IMO), so it's a slippery slope from a cost perspective.
Have fun.