There are a few ways to get troops:
1 - Keys! This is the main way to get troops. On console we still have iron keys, which cost 1000 gold, but have a chance of getting you any possible troop. You also earn keys as rewards from other things. Magic Keys are bought with gems - you’ll get a small trickle of gems naturally, but mostly you pay real money for the gems.
2 - Quests! Each kingdom’s quest line gives you an Epic troop when you finish it. This is a key way to get yourself a decent army early on. Do 5-6 kingdoms, pick the epic troop you like best, and build an army around it.
3 - Weekly Glory troops! This is something you should start doing ASAP - but it takes a bit of doing. Each week (on Monday) folks get glory, gold, etc for how well they performed in PvP during the following week. Earn glory each day for your current rank. Then each week a new troop is released, and can be purchased with Glory.
On console side, you can earn up to 16 glory a day from a #1 PvP rank, and it costs ~120 Glory to buy the troop each week. On PC/Mobile you now earn 3 glory per PvP win (in addition) and troops cost 300-500 glory to purchase. Console will be switching to match the PC economic model soon, but the key thing is that by the time you are level 30-50, you should be trying to PvP up in ranks each week to get that new troop.