When using clustered index, the rows of the table are sorted by the column to which the clustered index is applied. Therefore, there can be only one clustered index on the table because you can't order the table by two different columns.
Generally, it is best to use clustered index when performing reads on big data tables. The donwside of clustered index is when writing to table and data need to be reorganized (resorted).
An example of creating a clustered index on a table Employees on column Employee_Surname:
CREATE CLUSTERED INDEX ix_employees_name ON Employees(Employee_Surname);