Thinking about starting to use KeyChain....questions

I have never set up KeyCHain, but thinking about it. Seems like there are a lot of pros and con discussions. If I enable it, will it use the passwords that I have already established for various accounts, or will it make new ones? If it makes new ones, how will I know what they are and can I get a copy of them? Do "most" people feel KeyChain is as safe as other password programs out there? I just seem a little hesitant to take that leap.....Input welcomed. Thanks so much.

KeyChain doesn't "make" passwords (well, it does but that's different). It just saves the passwords you give it.
So use your regular passwords and they'll be saved.
This is NOT the same as when you , for example, tell Firefox to save passwords. Firefox saves it's own passwords.
KeyChain is more for application passwords... like the Twitter app, or Imessages etc.
Also it keeps your login password for things like Adium, and various other things.

Not sure, but was thinking that it would suggest numbers/etc but I always declined.....maybe that was Safari? Guess I wondered/thought that keychain developed all these numbers (and that was what was making it "secure").....

I suspect you have a bad understanding of what Keychain is. You are already using it (indeed, you couldn't log into your Mac without it). Safari, Mail, and other Apple or third-party programs that need passwords use Keychain, so if you've ever saved a password in Safari or in Mail, you are again already using it. It also saves the password to any Wi-Fi network you've ever joined that needed a password. I'll bet if you open Keychain Access, you'll see a list of stuff you didn't think was saved.

Keychain can, indeed, suggest passwords (strong ones) if you want it to (it will offer on new password fields), but this is strictly optional. You are always free to put in your own proposed passwords on new sites, though of course the site may require a certain level of sophistication in the password. The advantage of Keychain is that it uses iCloud (again, if you want) to sync your stored passwords to your iOS devices, so they can be filled in when you visit sites on those devices.

More information on Keychain can be found here: https://www.youtube.com/watch?v=Og2RA10HW6U -- it's from last year, but nothing much other than some cosmetic things have changed.