Perception, inference and verbal testimony are the primary ways of right knowledge.
How do we know that there is an object in front of us? We acquire this knowledge through direct sensory contact. This is perception.
And when we see muddy water in a river, we suppose that there must have been rains uphill. This knowledge we gather by inference.
The words of others in whom we have faith also convey to us true knowledge as, for example, when we believe that there is an elephant in the nearby city, on hearing of it from a reliable friend, though we might have not have actually seen it with our eyes. This is Verbal testimony.
It is said in many Hindu scriptures that the sources of right knowledge are direct perception, inference and testimony or spiritual texts.