Hi,
Do you want to use the second PC as a second monitor, or do you want to use the same keyboard and mouse across both PCs?
If it's the second option, you can use software like Microsoft Garage's "Mouse without Borders" or Input Director (I consider the latter—which is free—to be better).
https://www.microsoft.com/en-us/download/details.aspx?id=35460
Thanks.