It's a bit of a pain. Apple's Password will only import csv files and then only if the field titles match what Password uses which are: Title, URL, Username, Password, Notes, OTPAuth.
You can export a .csv from 1Password - so I suggest you select a couple of entries and just export them and play around with them. Open the file and change the column headers to those that Apple Passwords uses and try importing. If there are extra columns then Apple Passwords ignores them. It doesn't care if fields are empty.
I've tried this with my password manager and it works for entries which only have the Apple elements. But for things like email accounts my app has entries for SMTP host and other email-specific settings, which Apple Passwords can't handle. Ditto credit card details, passport, PINs, etc.; Apple Passwords is pretty basic and seems to be aimed at website/app log in and little else. I think you'll be hanging on to 1Password for a while yet.
I use Apple Passwords because it's integrated and convenient but my other password manager will be the main store for all my secure details until Apple makes its app more useful - such as for email, bank and credit card accounts. We'll have to wait and see if Apple develops it as a comprehensive tool or consigns it to the pile of stuff they started but lost interest in.
