What you do in this game is to keep going through a map until the map level is high enough to open up the next map. The map level also open up new materials. You use material to craft gears. Equip gears to your heroes to make them stronger. You get new hero by crafting a required gear (with any quality) that the hero wants. Gear quality is random after you successfully craft it. The better the gear, the longer it takes to finish crafting.
You can progress the game even while idling. Just pick the location you want to idle. You could also manually go into the map with your heroes to fight and get materials dropped. The higher the difficulty of the map, the more exp the map gains plus better chance to get rare materials.
I drop 1 star because the game has bugs. All bonuses that aren’t related to hero stats are not working. One is regarding exp bonus. The display of total exp gained after a battle is correct (with bonus exp) but your heroes actually gain exp without bonus included. For example, total bonus exp said 110%. A battle with monster is worth 90 exp, so the display would be 99 (+9) exp points. Your team consists of 3 heroes, so the exp is divided by 3. Each hero is supposed to earn 33 exp, but in reality each hero earns 30 exp.
I hope the bug is fixed (just hope)