It's safe to assume you open this guide because you have a problem with Crusader Kings II, so the first thing you must to do is open the game installation folder (\SteamLibrary\steamapps\common\Crusader Kings II\) and look for CK2game.exe, try to open it.

If the error messages are:

• The program can't start because api-ms-win-crt-heap-l1-1-0.dll is missing from your Computer. Try reinstalling the program to fix this problem.
  
• Other similiar messages

That means you have to download that dll file and 11 others!!!

But don't worry, guys, I have an all-in-one link download:
https://drive.google.com/file/d/1R6JOKqj-nW64HIH6VR7-jEgxxIX_Cu4b/view

Here's the installation rules:

[1] If your system is 32-Bit Windows, copy-paste the 32-Bit version files into C:\\Windows\System32\ only[2] If your system is 64-Bit Windows, copy-paste the 32-Bit version files into C:\\Windows\SysWOW64\ and the 64-Bit version files into C:\\Windows\System32\