What do non religious people believe in?

It greatly varies. Some believe in evolution, others believe in a God but not one who wishes to be served. Some non-religious people even believe in reincarnation, though this is rare as most people believing in reincarnation are religious.

The most usual alternative to religion is called secular Humanism, which asserts that we human beings have our own intrinsic meaning and value, and we should believe in ourselves; we do not need to derive meaning from supernatural beings such as God.

There are also some non-religious people who simply do not believe in anything, which is a philosophy called nihilism (from the Latin; nihil means nothing).