This is a button click event of a button called btnShareText
A very good way to learn App Inventor or Kodular is to read the free Inventor’s Manual here in the AI2 free online eBook App Inventor 2 Book: Create Your Own Android Apps … the links are at the bottom of the Web page. The book ‘teaches’ users how to program with AI2 blocks.
The property isPlaying returns a boolean , true or false, in your case „true“. So it is nonsense that you set the player source to it. You should really follow Taifun‘s links and do some beginnet tutorials to learn some basics. Also use often the search function because there are already answers to nearly every thing