Getting Started in Tempest Rising

GDF is the recommended learning faction — it's the most balanced, 'classic' RTS roster with standard infantry, tanks, and helicopters and no major gimmick to master first.
Tempest Dynasty units are faster and more mobile but cost more, so expect a higher-tempo, higher-risk playstyle if you pick it first.
The Veti are playable in multiplayer for free in the base game, but their singleplayer campaign (Veti's Wrath) is a separate paid expansion.
Skirmish vs AI supports 3 difficulty levels, a good low-stakes way to learn a faction before jumping into ranked multiplayer.