FileVault is the native macOS full-disk encryption app that's equivalent of BitLocker on Windows. Similar to BitLocker, it prevents unauthorized access to your Mac by encrypting the startup disk and requiring your user account password to unlock it at login.
Mac users are recommended to turn on FileVault to protect their personal information and sensitive data. When FileVault is enabled, it encrypts all the existing data on your hard drive and any new ones you create in the future with a secure 128 bit AES encryption method.
Simply put, the bad guy must have your password or recovery key to access the information on your Mac. Even if they open your Mac and take out the hard drive, they will only see the meaningless encrypted data and won't be able to decrypt it without the key.
However, FileVault isn't as convenient as BitLocker, as it doesn't encrypt external drives. If you want to encrypt your external storage media with the strong protection of BitLocker on Mac, you can download and install iBoysoft BitLocker for Mac for free. It also allows you to read and write to a BitLocker-encrypted drive on Mac.