In a nutshell, HelloSign can be used whenever you need to sign and send a document to someone.
Or, if you need someone else to sign a document, you can use HelloSign to request that person's signature and collect the signed document, all online.
With HelloSign, you do not need to print the document, fill it out, scan it and email/fax it back. You can do that whole process on your computer without any paper.
Here's a video that will give you a quick overview of HelloSign: