These terms refer to the ability of computer’s processor to handle a large amount of RAM memory.
In short, 64-bit (x64) is better than 32-bit (x86), because 64-bit can use more efficiently a larger amount of computer’s RAM memory, so your computer and programs will work faster.
When to install a 32-bit Windows operating system? When you have less than 4GB RAM memory.
What is the difference?
A 64 bit operating system it is able to use more than 4gb of RAM memory.
Conclusion: if you have at least 4GB RAM memory, go with a 64-bit version of Windows.
All 32-bit programs will work on a 64-bit operating system.