Extracted from the website of Buddhist Vajrayana Charity Funds Association and translated (洞察「識」) into English:

Discernment of Consciousness

Mind Consciousness (the 6th consciousness) determines the process of selection and cognition of the first five consciousness (eye consciousness, ear consciousness, nose consciousness, tongue consciousness, body consciousness).
Use a picture as an example, person A looks at this picture via the process of eye consciousness; however, gives rise to praise, review and other psychological activities which is the sixth consciousness. Similarly, person B looks at the picture via the process of eye consciousness, but feels disgusted, rejected and other psychological activities which is also the sixth consciousness. This proves that the mind consciousness of human beings is different and the reaction is therefore different!

Manas Consciousness (the 7th consciousness) is tarnished by the first six consciousness (eye consciousness, ear consciousness, nose consciousness, tongue consciousness, body consciousness, mind consciousness). The external view and inner feeling are captured by the first six consciousness.
For example, resentment, love and hate, good and evil, etc becomes greed, hatred, delusion, etc, which is the process of ‘self ego’. Therefore, it is also known as ‘Contaminated Consciousness’.

Alaya Consciousness (the 8th consciousness) collects the karma and karmic causes of all the good and evil deeds generated from the first seven consciousness (eye consciousness, ear consciousness, nose consciousness, tongue consciousness, body consciousness, mind consciousness and manas consciousness). Just like a large warehouse, each and every moment, the seeds constantly move in (karmic cause), as the fruits constantly move out (karmic effect). Human behaviour and feelings cannot exist on their own and cannot remain unchanged forever. Instead, they are in accord with cause and effect, birth and death, which are forever changing each moment. Hence, the eighth consciousness cannot be separated from the seed of karmic effect nor can it exist in isolation, and it is impossible to remain the same. This is similar to water current, which is the so called current, because its motion continues constantly, if the nature of constant continuous motion of water suddenly stopped, this would no longer be a current.

The sixth consciousness being the Mind Consciousness and the seventh consciousness being the Manas Consciousness form the original root of samsara in beings, and all karmic causes are saved in the eighth consciousness being Alaya Consciousness.