Password managers store logins, generate strong passwords and fill them into apps and browsers. macOS now includes the Passwords app built on iCloud Keychain, so a third-party manager makes sense mainly for cross-platform use, sharing with family or a team, or keeping a local offline database.
1Password and Bitwarden are well-known cloud-synced managers; Bitwarden is open source and has a free tier. KeePassXC, MacPass and Strongbox use the open KeePass format, which you store and sync yourself, and Strongbox is a native Mac and iOS app. Look for independent security audits, browser extension quality and passkey support.