I am also confused since I can hardly find any enemies to fight.

If there is a freelancer or start as a general or captain option in the future will be nice.

Start as adventurer
Recruit insurgents in villages
Fight bandits or patrols
After making enough money and levels from patrols, attack a city or army base

If you talk to a faction leader (like Queen Victoria) you can become a vassal for their faction. They seem to give you a town. Use the money from that to fight in that faction's wars.

I haven't seen any bandits or patrols. My map only has towns nothing else.

Once you join a faction as an adventurer, do you get access to their unit trees?