A parser converts a file full of source code into a data structure.
An interpreter traverses that data structure and executes the appropriate commands for each significant node in the structure.
A compiler transforms that data structure and emits something else. Perhaps this other is object code for a specific processor or perhaps it's binary code for a virtual machine or perhaps it's source code for another language entirely.
If you look at compiling and implementing languages this way, you already know the general technique. (everything is a compiler).