For all intents and purposes, a partition is a hard drive. When you make 3 partitions, you will see 3 hard drive icons on your Desktop.
You label them by clicking on them and changing their name. You install software on them by choosing them when you run an installer.
You can use Super Duper to clone from your internal hard drive to whatever partition you like on the external. You can upgrade to Mavericks by running the Mavericks installer, then choosing the partition you want to put it on.
