When you look at your self in the mirror do you believe that you are looking at your self yes or no if you believe that you are looking at yourself and no one can convince you other wise, that is how you must believe in Jesus Christ to save you, that is if you want to go to heaven, because there are not many ways to heaven only one.John 14:6 Jesus saith unto him, I am the way, the truth, and the life: No man cometh unto the Father, but by me.
There are two different types of belief: A religious belief and opinions such as assertion. Belief without evidence is pointless i.e. Opinions. In religious cases you should only have belief in GOD if you have proof. By saying for example Jesus is GOD or having that type of Belief in order to be sure, one would need to read the Bible and find out what Jesus says about himself and about GOD. John 10:29: My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of the Father's hand.
Belief is having faith in something, having trust, having philosophy and revelation of jesus christ! Beliefs helps us to distinguish what is morally acceptable and what is not acceptable, it also enhance our understanding of our culture and values. A good belief system promote and balance morally upright society's values.
It means what you belive in. It could mean you only believe in yourself and nothing outside of that (like a God)