Campaign section
The campaign is where you will be doing most of your battles and collection of evos, tokens, and items. Upon entering the campaign section, you will see sections of the map. Most will be locked off if you just started and have a level requirement to access them. When you select a section of the map, a stage list will appear showing the available stages.
On each of the stages panels, you will see the name of the stage, the Stamina cost to enter it, the hero token that may drop upon completion, and the stage ranking of one to three stars. On the background of the stage panel, you will see where the stage is set in. Seeing this will get you a general idea on what Elements you can possibly run into but this may not always be the case.
When you select a stage, you will see the unit composition of the stage. Pressing and holding the icons of enemies show what they are capable of. You can use a team specialized to fight them if you have heroes available, or you can usually brute force your way through them even if you are at a disadvantage provided you play smartly.
If you are having some difficulty beating stages, you may want to wait till you are a bit over-leveled or have more heroes to use that can effectively counter the enemies. Alternatively, you may look for a player who is strong so you use their hero in the sections that are giving you trouble.