Hello, I have this huge problem.
I'm supposed to make a LISP interpreter in C++ but I have absolutely no idea what the programm should look like.
So far I have a parser, which splits input string into the list of smaller strings (words, brackets).
Could anyone give me a small clue of what to do next?

Representatiom for atoms, conses, lambda expressions and special forms like setq.

Representations like what? You mean to create some sort of variables to store it?