Summarize the following:
External hard drives and other USB flash drives are sometimes formatted to work with one operating system (OSX or Windows) only. Depending on the computers you're transferring between you may need to reformat to a more universal formatting option (FAT32) before attempting the transfer. Using a storage device is one of the slowest methods for file transfer but may be the simplest to execute if you're feeling intimidated by the more technical methods.  If the storage device is recognized and the files are accessible on both computers, you can proceed. If reformatting is necessary you can find more information at Format FAT32  The limitation of this method is typically speed, as numerous large files will take a significant amount of time to transfer in this fashion. Check that you have enough space on the storage device to house all the files you'd like to transfer before beginning. Your best bet is to know in advance how much space you will need and to plan accordingly. This process will be like other file management on your laptop - simply drag and drop the files you need and wait while they are fully transferred to the storage device. Make sure to disconnect properly to avoid damaging the files, then drag and drop to the client laptop's desktop or another more appropriate location.
Find a compatible storage device. Plug the storage device into the server computer. Move the files to the storage device. Eject the drive and connect to the client laptop.