I have read through the FAQs and searched around the internet, but can't find the answer to my question. Hopefully I won't sound too stupid here.
If I use a router and someone finds my IP address, that will initially at least, be only my routers IP address, not the internal IP address of my computer. However, using that would they be able to find my internal IP address? How would they be able to find it? How could they make the jump from my router to my PC? And if it is done with "scanning" my router somehow, exactly how do they do that? Is it a hacker program or just commands? I've tried it from my friend's computer to my own and I can't figure out how that would work(of course that means little).
I'm trying to make my computer secure and an extremely knowledgeable friend of mine told me that routers are better than firewalls. But I don't want to screw myself here. Should I install a firewall as well?