What teaches the computer machine code?

Hey, first post, so please be gentle! ;-)

Just a general comp sci question. Say for example I have built a computer (just the physical wires etc) - what enables this electrical maze to then operate machine code? How does the computer know that or example 01011111 (or whatever) means fetch data from 01000111 (or whatever)

Am in right in thinking that assembly gets converted to machine code, and then the cpu follows this code?

Cheers everyone!