Rationalism: This is the principle that all knowledge can be gained through using reason and logic. It's like solving a math problem - you don't guess or use intuition; you follow logical steps to reach your answer.
Secularism: This refers to the principle of separation of government institutions and persons mandated to represent the state from religious institutions and religious dignitaries. Imagine if your school principal had no say over what happens at your local church, mosque or temple - that's secularism.
Humanism: This is an outlook or system of thought attaching prime importance to human rather than divine or supernatural matters. Humanist beliefs stress the potential value and goodness of human beings, emphasize common human needs, and seek solely rational ways of solving human problems.