Chances are you have been using another graphics application before. It might be Photoshop, it might be Gimp, it could be Corel Painter or Paint.net. Krita will seem very familiar to you at first sight, and then you might start noticing differences. Or wonder where some basic functionality hides. This pages lists the main user interface peculiarities in Krita.
Krita makes a difference between tools and brush engines that Photoshop or Gimp don't make