How do you formulate a perception?

you rely on previous information you know.
you recall old memories and evaluate them.
you experience the outside world through your senses.
your brain interprets the messages into a story.

You experience the outside world through your senses.

Explanation:

"The process of forming a perception begins with your sensory experience of the world around you."

Source:

http://thepeakperformancecenter.com/educational-learning/learning/process/processing-information/perception/forming-a-perception/

Other sources says similar if not exactly the same thing.

What are the components of perception?

This refers to a person whose awareness is focused on the stimulus, and thus begins to perceive it. There are many factors that may influence the perceptions of the perceiver. The three major factors include motivational state, emotional state, and experience.

Source:

https://explorable.com/perception