Add a USB drive to the USB port on your Mac.
Open the app called "Disk Utility."
Select the USB drive on the bottom left side of the menu pane. Note: Select the drop down menu at the top left (next to "Disk Utility") and select "show all devices."
Select "erase" at the top left to format the disk (make sure there are no files on the drive or you will lose them).
Select "Format" and then "Mac OS Extended Journaled." Under "Scheme" select GUID Partition Map.
Select "Partition" at the top menu bar. Select the (+) symbol beneath the pie chart to add another partition. Note: One partition comes with drives by default. Use the Pie Chart to select how much space you want to dedicate to the partition.
Select "Apply." On the left menu bar, you wil notice that you USB drive now has two partitions.
Caution: You must make sure to select the USB drive and not your hard drive by mistake or you risk losing the files you have on your computer's hard drive.
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