Simplistically, you plug one end of the RJ45 into the RJ45 port on the laptop and the other end into the RJ45 port on the desktop.
But, I suppose the real question here is - what are you ultimately trying to achieve by connecting these 2 machines?
OnePlus 5 review
Alice Saey's mesmerising animation for Dutch singer Mark Lotterman
iPad Pro 10.5in (2017) review
Comment booster votre iPhone ?