Welcome to the fórum.
first of all: In this game you don´t lose anything, your progress may be slower but never wrecked, so don´t worry much about mistakes, is part of the process.
DIFFERENT GAME MODES:
You have noticed that you have12 or 3 kind of flags on top of your screen, it is the energy available for each game mode.
They are World energy, Raid energy and Titan energy.
World energy allow you to fight in world map and adventures (IIRC adventures unlock at level 12)
Don´t worry much about going through the map, avoid using ítems at first, they are very expensive for what you can produce.
Raid energy the assault you can perform, at first rerolling is ruining, so try to fight what you meet, don´t worry about the cups, focus on learn (If you press over the hero you see their stats and skill)
Titan energy: The attack on titans you can perform, only available if you are in an Alliance, join one ASAP if you aren´t already, hit the titan, don´t worry if you get killed it is a team work. you Will get reward and resources very helpful.
WAR energy: This is a different pvp mode from assault, You have 3 flags and 3 after 12 hours in a 24 hours match. You can´t use same hero twice (you can use duplicates) So you need 30 héroes to give all your effort in war. I suggest you to uncheck the participación if you aren´t ready, it is very important to use all your attacks.
Feel free to ask any question in this thread.