Welcome to the community!
The tutorial is not completely finished and misses one important explanation: the retreat
button. It's at the very bottom-right corner of the screen, containing three little arrows pointing down. Each time you enter a battle, you get a chance to withdraw during your first turn. At the beginning of the game when your hero is still weak and your deck and team not fully built up, this is a mandatory strategy. You'll want to explore, find resources, build up strength, determine which party is the weakest to engage it first... and only then tackle tougher ones.
As you discover rooms with enemy parties, pay attention whether they contain a summoner or not, as they can play cards too and therefore be much stronger opponents. Besides the description on their card, you can spot summoners at their ornate lifebar. Also the icon on the map is different for rooms with summoners vs. rooms with regular units.
P.S. If you're a discord user you'll find faster response time to your questions on the D20Studios channel: https://discord.gg/d20studios
Also, would you mind changing the title of your thread to make it easier for others in your situation to find this answer? Thanks!