Selects your power, and will cycle through. When a unit is selected use this button to upgrade the unit, and also with a builder to select buildings. Opens up your menu, and allows you to buy powers. This will select all of your combat units on the screen, so there is no need to individually select each unit to attack, you can do so with every unit all at once. Keep yours at your home fortress and keep them well protected! There are certain levels in which you need to get a Hero to a certain level - see the Good Campaign level 2, but you will have no problem keeping him alive this early on in the game.
The second best advice I will give, is do not use your heroes! you do not want to risk losing a hero to some flukey arrow shot or another enemy hero. Before we start, the best advice I will give is play on easy, there is absolutely no point in playing on any higher difficulty, there are no achievements for difficulty, and you have absolutely nothing to prove by playing on a harder difficulty.
