The Minoans were the first sophisticated and uniquely Greek civilization that existed on the island of Crete c. 1700 B.C.E. Their capital city was known as Knossos, and contained a series of lavish buildings and palaces. Their civilization was remarkably modern with running water and flush toilets. They developed an alphabet known as Linear A, which used symbols representing syllables rather than ideas; and later establlished colonies on Cyprus. Their learning and architecture were very influential on the later Greek classical culture.
The Minoan civilization gets its name from their legendary king, Minos. They were not called Cretans, even though they lived on the island of Crete, as the name is too easily confused with "cretin," meaning "idiot."
The Minoans were a civilization that existed on the island of Crete from around 3500 to around 1100 BC. The Minoans were a forerunner of the civilization on the Greek mainland that came later.
If you are asking who the Minoans were in terms of what their ethnicity was, it is less clear. The Minoans appear to have been a fairly cosmopolitan people because of their geographic location and the fact that they had contacts with peoples from around the Mediterranean and beyond. It is thought that the Minoans were probably not and Indo-European people and were therefore not related by "blood" to the Greeks. Their society, and presumably their population, seemed to have a mix of influences from around the region.
The Minoans, then, were a major Bronze Age civilization that was centered on Crete and seems to have been rather diverse in terms of its society.