The confusing part was the non-idiomatic English "builds X to Y" instead of "builds Y from X".

Edit: perhaps it is idiomatic somewhere in the world to say "builds X to Y", but not in the U.S., in my experience. Could be similar to British "different to" as compared to American "different than" or "different from".

Is the program source is an instruction on how to run the program or how to build the program? What a compiler does with the program source?