surfacert

Hi! I have a surface RT. I downloaded an app which puts a slideshow of famous paintings as your locked screen display. A few days later it stopped working and paused on this terrible painting of an angel taking a dead man to heaven... so I went to change pc settings and changed the photo but...

I noticed the day I got this tablet/pc that it would not let me download anything from outside the app store! After reading and reading it seems impossible! Is this true or is there a solution to this? Also.. The reason I bought this tablet is because it's also a pc so I was able to use it for...