Some folks would prefer to partition first, with "fdisk /dev/sda", then create an "sda1" partition, and then mkfs sda1 instead of sda.
Some USB drives will likely come with with a VFAT filesystem on them at the outset, in which case you might want to leave that filesystem on it, by skipping step #3 above, and not partitioning. This is especially true if you want to use the drive for copying data between linux and other OSes.
Once it's mounted, you can copy files just like any other filesystem (EG with cp or a tar pipeline), but if it's a non-native-linux filesystem, there may be some differences in things like how filename case is handled, or length of filenames, or characters allowed in filenames.
I've yet to see a USB drive that came with a partition table on it - instead they didn't bother with a partition table and used the entire disk as one filesystem. (On most hard disks in the linux and microsoft worlds, but optionally really in the linux world, the first block holds a partition table, but if you don't need a partition table, then you can use sda instead of, for example, sda1).
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