As Buddha describes; YOU are made up of 5 different parts.
FORM - Eyes
FEELING - Happy or Angry
PERCEPTION - Relation to understanding
MENTAL FORMATION - Reaction to perception
CONSCIOUSNESS - Awareness to surrounding
This 5 aspects cover your physical and mental entity. Cannot understand and hard to digest? No worries i will break it up into simpler terms for you.
Example: you are at a shopping mall waiting for your friend.
Firstly, CONSCIOUSNESS allows you to know that the shopping mall is crowded. Then, you use your FORM (eye) to scan for your friend.
Then at the entrance, you see your friend. FEELING arises as you feel happy to see your friend. This is when PERCEPTION comes in. You know him for a long time and knows he will shake your hand to greet you. MENTAL FORMATION gives you the chance to react to what you are anticipating and you reach out your hand to shake his.
This 5 aspects allows us to interact with our environment. Different people have different stream of how they handle situations and this may lead to the 3 evils (greed, anger, ignorance). To counter this foul emotion, as Buddhists we must practice and lead life under the guideline of the 8 fold path.