To Take backup of your files from the plesk please follow the below steps:
1: Open the Plesk panel with the credentials you have received on your registered email id.
2: On right side of your Plesk there is an option named as "BACKUP MANAGER".
3: Once you click on it new window will open there is option on top named as"BACK UP".
4: Once you click on it Backup window will appear just click on OK at the end your backup will start generating.
5: Once the backup will be generated you just need to click on download icon.
6: It will redirect you to another window in that you can set the password for your backup downloading or you can just skip it.
7: After clicking on OK the backup will start downloading on your system.