How would I recreate a bullet with the spread and stuff like the shotgun in this game? I have looked around the internet but I couldnt find a good solution.
It is most likely that they use beams to achieve this this effect.
They can have a gradient added to them so they fade out and to use them simply have an attatchment at the origin (the end of the gun) and another at the mouse click location (where the shot is fired to).
Then simply create a beam with the two attatchments.
Acctually taking damage can be quite complex. It requires the use of Remote Events so the client can interact with the server. There are plenty of tutorials out there for creating weaponse/guns. It is simply too complicated to explain in writing.
You could try on of the following tutorials which is very good and then impliment the beams that I mentioned from above.