This command selects all members of the set that is associated with the given
keyis associated with a value that is not a set, an error is raised.
keydoes not exist, no value is returned.
Returns all members of the given set.
$ SADD yuga_world "Africa"
$ SADD yuga_world "America"
$ SMEMBERS yuga_world
1) "Africa" 2) "America"