Firstly,check the ghost shooter tutorial for an introduction of how to use Construct 2.
I learned construct 2 from there and moved to templates etc...Manual is also very good.
Anyways,since you asked,
How do I make my charater shoot bullets and fireballs.
And how do I make the scores and health follow the screen.
1-To fire bullets,you need to spawn an object(On where you want) when mouse or keyboard key is clicked.
2-To make score,health follow the screen,make another layer,set parallax to 0.And put all the health and score there.