If you are not sure what QuickSync is, check this article.
Let us first of all check if QuickSync is already available for you. Open up your OBS and go into the settings and then into the Encoding section. Below is an example screenshot of how it will look if QuickSync is not yet enabled on your System.
If this is the case, and you cannot select Quick Sync in OBS, you will have to make sure the integrated Graphics Chip of your System is activated in your Bios. Now this, unfortunately, depends a lot on the Mainboard you are using and the company that produced it. You will have to check your Mainboards Manual but I can show you some examples of what option you are looking for:
As you can see it's often called "*** Multi-Monitor" or in the middle example it's just called "Internal Graphics". If you cannot find a similar option in your Bios it might be that your Mainboard does not support the Quick Sync feature. You can, of course, contact and ask your Computer or Mainboard manufacturer for more info. But let us assume you found the option and have activated the "Multi-Monitor" feature of your integrated GPU. After Windows has booted back up you will want to download the latest Intel Graphics Drivers for your Processor generation. So for example if you use an i5-2500K you would search for the second generation Intel Processor Graphics driver, with an i7-3770K you would search for the 3rd gen and with a Haswell i7-4770 it would be the fourth gen. Sometimes the driver also supports more than one generation. The Intel Download Center is your friend when it comes to getting the latest driver.
After the driver installation finished you will want to reboot/restart your computer once more and then you should be able to activate the Quick Sync option in OBS.
The general encoding options you have available of course stay the same. So you can use constant bitrate for streaming purposes or use a variable bitrate and crank up the bandwidth for local recording. But in the advanced settings of OBS, you can now change the QuickSync preset instead of your x264 encoding preset. In some cases lowering the preset can be useful if you encounter problems while encoding. Just configure everything to your liking and then start a first preview. In some cases you might encounter the following error:
Do not panic, this error is normal on some system combinations and the older generation Intel Processors. It simply means the integrated Graphics Card needs a Monitor connected to "be" active, but again, do not panic! We can just fake it! Just follow the instructions to connect a "Virtual" or fake monitor and after you are done the error should be gone and you are ready to use Quick Sync.
As a short sum up: You need a Mainboard and Intel Processor that both support Quick Sync. Then activate the necessary functions in your system Bios and install the Inel Graphics drivers. On older QuickSync versions you might have to fake connect a Monitor (you can also use a real monitor if you want to). That's it. Have fun using Quick Sync for your recordings or even a live stream and be happy about a lot of free CPU power for your Programs or Games.