You will get the basic concept of SaaS from this one. And the explanation is quite well said by the narrator explaining the topic. I definitely suggest you see through it , catch the terms and then let these terms be a googling aid for you to learn more on this.
Also you can explore good websites who have built their business well on the SaaS concept.
This one is a bit old but good enough for short intro into really basic level intro to SaaS
Software-as-a-Service in your Business
This goes one level further and does a little more explaining on SaaS and how it is useful to business.
This is a SaaS based commercial product. See it to learn more.