Q: How do I make my own add-ons?
A:
If you can't figure this out on your own you will never be able to do it.
Out, this is not true.
I would suggest looking at scripts such as the default gun and just see how they work and when you feel confident about understanding them, try it out. That's what I did and I am on my way to scripting a working weapon.
I also found playertypes the easiest to script so I would suggest working with them. REMEMBER: do not edit the original file. Always make a new one.
Also if you ARE on a Mac computer (which you probably aren't) I can give you help on how to turn text edit files into .cs files and .txt files.