If you want to add extra security to your Mastodon account, you can optionally use "Two-Factor Authentication" (2FA). When you have this feature activated, even if someone else finds out your password they will be unable to log into your account.
There is a complete guide to activating 2FA on Mastodon here:
➡️ https://fedi.tips/using-two-factor-authentication-2fa-on-mastodon
This guide also answers lots of common questions about two-factor authentication 🙂