Since you are new to this game so first
Now you queried about some things of this game,so here are the answers:-
1-Leadership(that blue colour crown) decides how fast your morale recharges in battle.having a high leadership is generally desirable because it helps you to attack on tough bases.you can increase your leadership by choosing appropriate items from granny store or by increasing your hero level.
2-scream boost(one of the best powers anyone can have) help you target specific things during battle.suppose you use scream boost(by clicking on the hero symbol at the top left corner of the screen) during a battle then all your units follow you till scream has its effect and it increases the fire rate of your units also.you can target any tower,blockade or any other enemy unit by just moving towards it and by clicking scream.
3-shield(which is on a sword) indicates that It will provide you extra protection from normal attack by knights and palladins.
If you want to know each and everything about the game,this is possible by two ways:-
1-post you any query here,believe me masters of the game are present in this forum.they will give you answer to each of your question and also help you to improve your skills.
2-go to royal revolt wiki by typing royal revolt wiki on google.there you will find information about every components of your kingdom.