Why are Carbon atoms the most versatile molecular building blocks used by living organisms?
See this old answer.
It is quite that remarkable that carbon should offer such a rich and diverse chemistry, and you are right to ask why. Carbon has the ability to catenate, to form long chains. And of course, along the chain there can be heteroatoms, nitrogen, oxygen, sulfur, halide, etc. that can modify the chemistry. All of these are modified and utilized in biochemistry. Anyway, check a library for the work mentioned in the linky.