Depends on what you're building, boards tend to be done as net lists (essentially a list of components and wires and how they are connected) - but digital chips

Depends on what you're building, boards tend to be done as net lists (essentially a list of components and wires and how they are connected) - but digital chips of more more than a few dozen gates are normally written in a highlevel language (linked to by other posters here) which can be compiled into both machine code that can be simulated, and synthesised into gates and wires (a net list) that can be laid out onto a chip