By default, most computers come with one partition and one volume on that partition. Well, in OS X there’s also a recovery partition, but that’s hidden so we’ll pretend like there’s just one. You can create additional volumes, which are useful for a number of different scenarios. The operation of creating partitions usually involves resizing a partition. That can be somewhat dangerous, so make sure to backup your Mac before doing so. To create an additional partition (and by default an HFS+ filesystem on that partition), first open Disk Utility from /Applications/Utilities. Note that by default, the boot volume is highlighted. You can’t create a partition inside a volume or…