These tools work in the same way as in my previous reply: a file is uploaded somewhere and the recipient receives an email with the download link. A possible disadvantage of these tools, as compared with a do-it-yourself "upload and send link" technique is that these free tools usually impose a finite lifetime of the file to be shared: the recipient has a week or so to download before the file is deleted.
Admittedly this rarely is a problem, but it's worth keeping this restriction in mind.