This is not the kind of question to ask here. No one will write an entire script for you. This site is for asking specific questions about specific problems.

However, I will point you in the right direction:

Check out the evac city tutorial (top down shooter) for the exact behaviour you want HERE

Also see THIS ANSWER for another way to achieve this.

To make the bullet appear you will need to use the INSTANTIATE function. The second example in the link has a projectile example.