When I tried Site Administration > Logs, I got an empty page opening.
Yes, I can see the issue. But I can’t see the cause. Check your web server logs. They will have an error message that will tell us the exact problem.
The web server logs are almost always the first place to look when you get a completely blank / white page.
As a new Mac user, you will find using Firefox lets you save username/passwords for websites but Safari doesn’t.
Safari seems to save passwords OK for me, or rather Apple’s Keychain does. But I don’t actually use that anyway.
As I use as many browsers as I can get my hands on (for testing / development) its easier (and safer) to use an independent password manager. My preferred is LastPass. But thanks for the thought 🙂