Buy the god pack. It's not on sale anymore but still worth it at $30.
If not save up for GODS that fit the roles you prefer and buy one that looks interesting. The game is balanced enough that everyone is viable right now. Tourney play is really the only issue when it comes to balance.
Buy the god pack.
Typical meta is this:
Duo lane (Long lane, on the same side as GOLD FURY, notable for the long distance between each team's tower) Support (Guardians) + ADC (Hunters)
Middle lane - Mages
Solo lane (Short lane, FIRE GIANT side, notable for the short distance between each team's tower) - Bruisers (Warriors) and a small handful of mages, but less so currently.
Jungle - Assassins and a few magical gods go here (Freya, Ao Kuang)
Now, much like DOTA and LoL some gods can go into lanes that don't quite fit the meta, but that's not really important as a new player.
Anyway, I like to use Arena or Joust to learn how to play a god, then take them into Conquest once I feel good with them, but some people just go straight into Conquest after bot matches or something. It's whatever really.
Learn how to hit your skill shots. Learn the shop, it's simple. Learn how other gods work. More complex shit I suggest watching tutorial videos or asking for help, but coming from DOTA I would imagine a lot of the conquest gameplay is similar, minus dealing with buff camps.
BUY THE GOD PACK.