Your ISP (Internet Service Provider) is the company to pay to give you access to the Internet (some here are free, but the principle is the same). In your case indeed Optimum Online.
If you can make a dial-up connection to MSN, then you also use MSN as an ISP. Only you can tell if it's necessary to pay for something you rarely use. As I said, here (in Holland) I would opt for a free alternative, but I don't know if those are available where you live.
IE6 is your browser. It comes with Windows. Firefox is another browser, which you must download and install yourself (Opera and Netscape are still others). Once you are connected to Internet (either by cable or by dial-up) you can (in principle) access all of it with any browser you like.
There might be exceptions such as some pages at Optimum's site specifically meant for its own members. And to prove you're a member must be connected directly through them. But, as I said, that's a BIG exception. Another exception is Windows update, which only works through IE, not through Firefox.
Outlook Express (not to be confused with Outlook, which is part of the MS Office Suite, which is far from free) is a socalled 'mail client'. Firefox isn't, but they have a program called Thunderbird (also free), which is equivalent to (some say: better than) Outlook Express. Other people use Eudora or Pegasus.
So, in fact, you never pay for your e-mail client program, nor do you pay for your browser program (unless you prefer the paid version of Opera or paid version of Eudora, but why should you).
But you might need to pay for the email-service used. That's the part after the @ in your email-address (your email-provider). If you're email@example.com, for example, that's hotmail. The basic hotmail is free, but you can get extended service (more space) if you have a paid subscription. But an @verizon.com address, to name something, might never be free. If you've got a subscription with an ISP (and you have two), an email-address is practically always included in your subscription fee. So I suppose you have two email-addresses, one at optimum and one at msn. Again, it's your choice to have 1 or 2 or 3 or 4.
All 'independent' (like Verizon or Yahoo or Gmail)email-services can be used from any connection. Most email-services that come with your ISP internet subscription can only be used when connected through that ISP. That doesn't have a technical cause, but it's just their policy.
Your last question: if you are going to use a new email-program you have to tell some data on your mailbox with the email-provider. That are a pop3-server, a smtp-server, your username and your password at least. In Outlook Express you can find them under Options>Accounts, but that's different with each program. And you don't see your password, but just *******. But your email-provider can always tell you what you should fill in.
Hope this help, and post again if things aren't clear. Other people will tell about the same in different words, or tell more.
With all the hype lately about Firefox, I am again looking into what is best, overall. I immediately became confused. I am trying to understand what/who is my ISP, what is my browser, what is my e-mail provider, etc.
I gain access to the internet via a cable modem. The company is Optimum Online. Is that my ISP? I pay a monthly fee for the service.
However, I also subscribe to MSN, for e-mail and internet access. For MSN I also pay a monthly fee. If the cable modem goes down, I can use MSN dialup. Would MSN then be my ISP?
Is it foolish to pay two fees (one to Optimum and another to MSN), because the cable is only very rarely unavailable?
I also use IE6. Is IE6 my browser?
It seems that I can get to the entire web via IE6. (Or Optimum, for that matter.) It also seems that I can use Outlook or Outlook Express for e-mail. There seems to be no fee associated with IE6, or with Outlook. So, again, am I being foolish to pay for MSN?
If I use Firefox as a browser, it appears that I can get to the entire Internet. No fee. Does Firefox serve the same purpose as IE6? (Excpet that many say Firefox is better.)
Now suppose I use Thunderbird for e-mail? There seems to be no fee there, either. Again, am I being foolish paying for a service that is free elsewhere?
Now for some technical questions: While trying to set up Thunderbird, I am asked for my e-mail system (or something like that). I think it is supposed to be something like "firstname.lastname@example.org., or SMTP..." Where on my computer do I find what the e-mail server is? I think I have looked in the obvious places, but I see nothing that looks like it will answer the Thunderbird prompt. I think it used to be in "Accounts," but I don't see it any more.
I know this is a really long question, and I should have learned this stuff ten years ago, but I never did really grasp the concepts.
Now, if anybody has read this far, is there a tutorial somewhere that explains all this stuff???
Thanks for your patience,