Samsungs aes encryption is always active but to be effective you will need to set an ATA password for the drive in the bios in the security section. Simply enable “Password on boot” and set an “HDD Password.” Administrators also have the option of setting a “Master Password,” which can allow a lost user password (“HDD Password) to be recovered. The “Master Password” may also be used to unlock and/or erase the drive (depending on the settings), effectively destroying, and thus protecting, the data but allowing the drive to be reused. The setup procedure may differ slightly depending on the BIOS version installed on your particular machine. It is best to consult your user manual if there is any confusion. Please keep in mind that not all Systems support ATA AES drive encryption.
edit - and as always, before you make changes which will affect your storage, please make a backup before making the changes.