To understand the difference we need to first know the type of processor used in computers. It really comes down to the processor type, which are usually 32-bit and 64-bit.
To make it simpler, think of it this way, a motherboard has 32 lines going to the processor. Another motherboard has 64 lines going to the processor. Which do you think will transfer information faster simultaneously.
Processors can handle large bits of data simultaneously. 32-bit processors can handle around 4GB of RAM. 64-bit processors can handle larger amounts of data, around 8GB of RAM and higher.
So if the hardware meaning the processor is 32-bit, the operating system such as Windows also needs to be 32-bit.
If the processor is 64-bit then you can have either operating systems, 32-bit and 64-bit. Installing a 64-bit Windows Software with a 32-bit processor is not possible. Why? Because the hardware is the first thing which should support the software.
How to know if you use 32-bit or 64-bit operating systems?
If you are using Windows, right click on My Computer icon on the desktop. Read the System details. The 4th Point System type will mention the type of operating system you are using.
Why should you know this?
For you to decide which Windows to install. If you are planning on installing an Adobe software to do graphic intensive or related work, or play games, video editing, or do other tasks which require speed and processing power, then it will be better to install a 64-bit operating system, like Windows. Just make sure you processor is 64-bit too.
32-bit processors are not an ideal option for tasks which are graphic intensive or require more processing power. Tasks such as designing, editing and gaming. Whereas 64-bit processors are best for these multi-tasking activities. These days usually most operating systems come with 64-bit.