3 FPS controller button layout questions

(hmm i've asked 3 questions in 2 days... go me...) So as i've said in my other two im using the first person controller prefab and all that comes with it, and i've added some scripts for shooting and everything is working fine. I know about the Input manager for buttons (just how to open it) and i have 3 basic questions

1: Can i add in more buttons, like fire1 is the mouse click, could i add in my own like firenow and have it be the shift button

2: What are the names of buttons, i.e. in the Fire1 where it says positive button [left ctrl] what are some other names i could put there, like if i want enter to be one, do i just type enter?

3:whats the difference between positive and negative buttons?

1: Yes you can. In the Input Manager you see the Size on top with a number behind it. Increase this number to create new axes. You can then modify your newly created axes just like you would with the existing ones.

2: You can find the most common names of buttons in the documentation (documentation link). Check the bottom of this page for the button names.

3: Negative buttons are usually used when your axis is mapping a movement direction. A negative button for the horizontal direction would move you in one direction while the positive button moves you in the opposite direction. If you need something trivial as shooting a weapon or jumping, etc. just use the positive button and leave the negative button blank.

Sebas pretty much summed it up - you can simply change button name new ones for example if you wanted to shoot using the "x" key - simply put x as the positive value

if you want to know the name of all the keyboard, mouse, and joystick keys, check out the reference.