Maslow’s hierarchy of needs

Physiological needs
These are biological needs. They consist of the need for air, food, water, sex, sleep, homeostasis and excretion. They are the strongest needs, because if a person were deprived of all needs, the physiological ones would come first in the person's search for satisfaction.

Safety needs
When all physiological needs are satisfied and are no longer controlling thoughts and behaviours, the need for security become active. Adults have little awareness of their security needs except in times of emergency or periods of disorganization in the social structure. Children often display signs of insecurity and the need to be safe.

Need for love, affection and belonging
When the needs for safety and for physiological well-being are satisfied, the next class of needs: for love, affection and belonging can emerge. Maslow states that people seek to overcome feelings of loneliness and alienation. This involves both giving and receiving love, affection and the sense of belonging.

Need for esteem
When the first three classes of needs are satisfied, the need for esteem can become dominant. These involve needs for both self-esteem and for the esteem a person gets from others. Humans have a need for a stable, firmly based, high level of self-respect, and respect from others. When these needs are satisfied, the person feels self-confident and valuable as a person in the world. When these needs are frustrated, the person feels inferior, weak, helpless and worthless.

Need for self-actualization
When all of the foregoing needs are satisfied, only then are the needs for self-actualization activated. Maslow describes self-actualization as a person's need to be and do that which the person was ‘born to do’. “A musician must make music, an artist must paint, and a poet must write." These needs make themselves felt in signs of restlessness. The person feels on edge, tense, lacking something, in short, restless. If a person is hungry, unsafe, not loved or accepted, or lacking self-esteem, it is very easy to know what the person is restless about. It is not always clear what a person wants when there is a need for self-actualization.

A simple diagrammatic representation of the pyramid can be seen here.   An elaborated version is here.  Another version is here.

References:
Wikipedia Maslow's hierarchy of needs
Wikipedia Abraham Maslow