Error:

Add object to the mutable set

[mutableSet addObject:@"One"];

Filter set using predicate

NSMutableSet *people;
// people contains objects with NSString property "city"
NSPredicate *cityPredicate = [NSPredicate predicateWithFormat:@"city = 'Vancouver'"];
[people filterSetUsingPredicate:cityPredicate];
// now people contains only people from Vancouver

Remove the object from the mutable set

[mutableSet removeObject:obj];

Remove all object from the mutable set

[mutableSet removeAllObjects];

Add multiple objects to the mutable set

[mutableSet addObjectsFromArray:[NSArray arrayWithObjects:@"One", @"Two", @"Three", nil]];

Union of the mutable set and another set

[mutableSet unionSet:anotherSet];
// now mutable set contains union of both sets

Intersection of the mutable set and another set

[mutableSet intersectSet:anotherSet];
// now mutable set contains intersection of both sets

Substraction of the mutable set and another set

[mutableSet minusSet:anotherSet];
// now mutable set contains only objects that are not present on anotherSet

Assign another set to the mutable set

[set setSet:anotherSet];