This is called Tanwin or Nunation. In dialects they don't care about much such vowels (and barely say any) but in standard Arabic it is important. Tanwin can be considered as a marker for indefinite noun; e.g. [The (f.) doctor: الدكتورةُ : ad-duktúratu] while [a (f.) doctor: دكتورةٌ : duktúratun]. I see they didn't put the sign above the endings of the words above and the truth is when we write Arabic in daily life we don't use these vowels markers unless it is necessary to explain something or avoid confusion.
Note: Tanwin can be in all vowels; -un, -in, and -an. It depends on the grammatical status of the noun.