That is an absolutely epic vision of a fantasy landscape.
Something out of this world... I love it!
Splendid work, fellow deviant, and congratulations on the Daily Deviation!
Not the artist, but would suggest you study the programs you would work with professionally, so either Photoshop or Clip Studio Paint.
GIMP is free and runs on almost anything, but if you can affort PS or CSP you should get them instead.