USB Loaders are able to use any FAT32 or NTFS formatted drive to store games.
If you use a FAT32 or NTFS drive, you will probably not need to make any changes to the drive in order to use it.
Optionally, you can divide the drive in multiple partitions and store your games on one of them.
We do not have a guide on this currently, but there are many guides on this subject on the internet already.
Make sure the partition for the games is marked as primary and active.
Also note that some loaders (mainly GameCube loaders) require that the games are on the first partition of the drive.
To place games on the drive, use any USB loader.
You can also use a WBFS manager that supports it, like Wii Backup Manager.