We need to understand it with Yogic perspective too as Shivananda writes in Kundalini Yoga.
Chitta is the mental substance. It takes various forms. These forms constitute Vrittis. It gets transformed. These transformations or modifications are the thought-waves, whirlpools or Vrittis. If the Chitta thinks of a mango, the Vritti of a mango is formed in the lake of Chitta. This will subside and another Vritti will be formed when it thinks of milk. Countless Vrittis are rising and subsiding in the ocean of Chitta. These Vrittis cause restlessness of mind.
Why do Vrittis arise from the Chitta? Because of Samskaras and Vasanas. If you annihilate all Vasanas, all Vrittis will subside by themselves.
When a Vritti subsides it leaves a definite impression in the subconscious mind. It is known as Samskara or latent impression. The sum total of all Samskaras is known as “Karmasaya” or receptacle of works. This is called Sanchita Karma (accumulated works). This Karmasaya is burnt by highest knowledge obtained through Asamprajnata Samadhi.
During concentration you will have to collect carefully the dissipated rays of the mind. Vrittis will be ever-rising from the ocean of Chitta. You will have to put down the waves as they arise. If all the waves subside, the mind becomes calm and serene. Then the Yogi enjoys peace and bliss. Therefore real happiness is within. You will have to get it through control of mind and not through money, women, children, name, fame, rank or power.
Samskaras are already discussed here,
http://www.theholisticcare.com/forums/viewtopic.php?f=16&t=2754