ERA: I am 99% sure this is how it works but I would double check.
You take the earned runs for the pitcher. Lets say 2.
Then take how many innings he pitched that game. Lets say 6.
That means the pitcher has an average of 2 earned runs for every 6 innings. Then you have to find out how many earned runs he would get if he theoretically pitched 9 innings, which would be 3. So the pitchers ERA is 3.
My Freshman year in high school I managed to pull off an ERA of infinite after my first appearance, figure that one out.
Better luck next time though Fresh.