Be patient. Posting again so soon will make people not want to help you as most people consider it to be annoying.
As for your question, unless you don't own the router that you used with Comcast, you can use the same one with Charter. They are not ISP-specific, though some companies do change the firmware so that it says their name and maybe has different options. Even so, it will work with any ISP.
If you do get a different router, then read the package/instructions that it comes with. It will tell you the router URL and default password information. Usually, you'll use
http://192.168.1.1 to connect to your router, regardless of what router you have. The default login may be blank, or may be "admin", or something else depending on the router. That's why you should read the instructions. Of course, you can also just go to
http://www.portforward.com/ as suggested and it will tell you the URL and default password when you choose the router that you are using.
