The harkot of last letter of  اِسْمٌ  is changeable, the sound at the end is sometimes ‘u’, sometimes ‘i’ and sometimes ‘a’. let’s see some common example-

We just saw مُحَمَّدٌ  and اللهُ  comes with a different look, at the end sometimes zer or zabr and sometimes pesh. This changes of ism  is known as الإِعْرَابُ    . Lets take the previous sentence to understand the change of Ism.

According to Arabic grammar-

بِلَالٌ   this is  مَرْفُوْعٌ (nominative case) of ism, ism will have pesh at its end.

حَامِدًا  this is  مَنْصُوْبٌ (objective case) of ism, ism will have zabor at its end. *   

خَالِدٍ   this is مَجْرُوْرٌ (possessive case  ) of ism, ism will have zer at its end.

thus, we will remember,

But for some ism this change is two types, they do not take tanween and the majrur state will also have jabr instead of jer. They are called   الْمَمْنُوعُ مِنَ الصَّرْفِ   or “diptote” , example- girls name فَاطِمَةُ،  مَرْيَمُ   , again some boys name, أَحْمَدُ , عُمَرُ  etc.     

Again, some ism doesn’t change, these are called “mabni” , example-  هٰذَا