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.