Having partitions on a hard disk works like, although not exactly the same as, having different hard disks.
If your computer has unallocated space on a hard disk, you can create additional partitions from the unallocated space after logging on as an administrator. If a hard disk space is fully allocated, unallocated space can be generated if the size of a partition is reduced or a partition is deleted.
One of the main objectives of having partitions in a hard disk is for separation of user files from operating system files. By keeping user files in a separate partition from another that hosts the operating system, user files can usually remain intact if the operating system needs to be reinstalled. If you need to prepare for a multi-booting setup from a single disk, it would be ideal to have a separate partition for each system. Other than these purposes, you might also want to refer to other benefits for disk partitioning as described here.
Some users may prefer Windows’ built-in Disk Management utility to manage partitions, but most average users will like third party or standalone partition managers, which are usually equipped with more features and easier to use in general.