One table can only have only one clustered index.
One table can only have many non-clustered index.
A clustered index requires no separate storage than the table storage. It forces the rows to be stored sorted on the index key.
A non-clustered index requires separate storage than the table storage to store the index information.
A table with a clustered index is called clustered table. Its rows are stored in a B-Tree structure sorted.
A table without any clustered indexes is called non-clustered table. Its rows are stored in heap structure unsorted.
The default index created as part of the primary key column is a clustered index.