How do accounts and sign-in methods work?

Your account is your email address. You can sign in with Google or with email and a password, and both lead to the same account when the email is the same

• Signed up with Google and want a password too? Open Settings → Account and click Create password. Air9 emails you a link to set it
• Signed up with a password and want to use Google? Click Continue with Google with the same email address. Your chats and files are all there
• New password accounts confirm their email first: open the link Air9 sends you, and you are signed in

A different email address is a different account, with its own chats, files and plan. Settings → Account shows which email you are signed in with