How do two processors work in a dual processor motherboard?

Question

Processors

How do processors work in a dual processor motherboard? This is a dual chip motherboard. Is overall computing power doubling? Is it possible to achieve the same result by connecting two PCs on some kind of high-speed bus? And it's also curious whether any x86-64 processors can be combined in this configuration or only a certain brand? Are there motherboards for three processors? Is it possible to assemble several processors, let's say the latest version of the intel i9, and make a supercomputer on this basis?

Answer 1

And it's also curious whether any x86-64 processors can be combined in this configuration or only a certain brand?

slot compatible.