SimpleNames are optional aliases you can give Items that make it easier to remember/say Item names. This makes it easier to control all of your devices, especially via Alexa. For example, if you have an Item named "Kitchen - 2nd Light Left", you can add a SimpleName "Kitchen Light 2" so Alexa will have an easier time understand it and you can remember it more easily.
After establishing a Connection SimpleCommands adds Items from that Connection to you Item List. Sometimes these Items have already been named by you via one of your third-party accounts (E.g. SmartThings lightbulbs), and sometimes we here at SimpleCommands have preset names for the Items (E.g. Lyft and Spotify). Want to address an Item differently than SimpleCommands currently allows you? Just create an SimpleName with whatever name you want so that your communication with SimpleCommands really is on your terms.