Ever wondered, what a digitally signed document means and how it works. Well here is a brief explanation through some pictures. Its from a lay man's point of view. If you are more interested in knowing the next level of technical details, have a look at the next slide which is technically more accurate.
Technically, more accurate depiction
Several free desktop softwares and online web applications allow you to digitally sign documents. for example, HelloSign, is a chrome plugin, which allows you to digitally sign documents, without leaving gmail.