From your question and comments I think you're a little unclear on what's happening. I'm not sure how to teach you how to run your router, i think you need to talk to someone near you to show you these things.
Port forwarding is when your router allows outside machines to initiate connections to a machine on your network. It doesn't allow any special access to the router internals, just a connection to your inside machine.
The security issue here is not your router, but your machine. Before, it was invisible to the Internet, and therefore somewhat safe. Now the internal machine can be reached. Is your internal machine safe? Is it patched? What's on that port?
As far as your specific questions:
They always know your external IP address. Any connection you make to someone will show your external IP address. I can try to ping the entire Internet (and with a botnet, some people try) and find your external IP address. If you're connected to the Internet, the external IP is exposed. Also, this has nothing to do whether your ports are forwarded or not.
A hacker can not access you through the forwarded ports. But your router may be set up to allow configuration on a web port. How to set this up is different for each router, but make sure anything similar to "allow configuration on WAN" is disabled. Allow LAN configuration only.
This is a hard question. Most routers are just routers. They do not know what an Attacker is. They're too dumb to know "good guy" from "bad guy". Some routers also have Firewalls. They know certain bad guys, and will filter those out. But your router probably has no filters on this port. If anyone tries to connect, they're probably let in.
Also, in your comments, you ask a lot of questions. The tradition here is to take new questions out of comments and as separate questions. Please try to ask your MAC filtering questions in a new question.
Good luck. Security is very hard. Even the experts don't get it right every time.
2This question is very broad. I think you need to do some research and if you get stuck on a more specific point, feel free to ask :) Please don't read my comment as rude, it's not meant to be! The security with port forwarding goes further than the router! – Dave – 2013-03-05T14:50:21.710
Any broad answers are fine. I just want to know how vulnerable I am with port forward open. And if anyone can search for ports and connect to my router/laptop. – avsdvsdd – 2013-03-05T14:51:12.717
1Yes, people can search for your ports etc. As I said, you may want to secure your PC and not your router. If you open something to the outside world for yourself, people you trust etc means you've opened it to all! In regards to broad questions, they are also considered off topic here. The more specific the question, the better it is for this Q & A site. – Dave – 2013-03-05T14:56:14.530
I do have mac filtering set up. So if a hacker gets through my port, he can just get through router cleanly without even having to guess the WPA2 password? – avsdvsdd – 2013-03-05T15:05:45.960
Are you there Dave? – avsdvsdd – 2013-03-05T15:14:04.233
2@avsdvsdd This is a question/answer format site. Question/answer isn't live chat. And that isn't what comments are for. – killermist – 2013-03-05T15:15:28.667
I am a newb, but thx for reminding. I just wanted to get the question answered. – avsdvsdd – 2013-03-05T15:16:35.713
All I will say is don't panic. The ports are opened to play games, I assume millions of people world wide do this. There typically is no point in hacking a user like yourself unless you happen to host a database of credit card numbers of similar. I do suggest you actually do some research yourself though. – Dave – 2013-03-05T15:22:32.630
What if someone is targeting me? If someone scans the port, and gets in, what are the ramifications? – avsdvsdd – 2013-03-05T15:23:14.597