Is it the one cPanel produces? If so, you have to unpack it first. Inside the tar archive is a folder called homedir that has all of your files, and a folder called mysql that contains your databases. The backup page in cPanel has an option to restore the database backups. Just select each file you want to restore and it'll create and populate the database. The files you can just upload with FTP or file manager. Odds are the ones you'll care about are the public_html folder. There's no need to restore the .folders (they're cPanel system data typically).