Please help me

// You can create an empty mutable dictionary this way
NSMutableDictionary *mutableDictionary = [[NSMutableDictionary alloc] init];

// There's also a slightly shorter form:
NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionary];

// Bonus: You can also do this :)
NSMutableDictionary  *mutableDictionary = @{}.mutableCopy;

// There are way more initializers, for a complete list, check the Apple Docs

// Immutable dictionaries can be initialized and populated with literal syntax 
NSDictionary *dictionary = @{ @"key" : value,@ "otherKey": value };

// Unfortunately that is not possible for mutable dictionaries, so we
// could use the `initWithDictionary` initializer with the dictionary
// we created before...
NSMutableDictionary  *mutableDictionary = [NSMutableDictionary initWithDictionary:dictionary];

//..., but what the assignment really expects is a one-liner
NSDictionary *mutableDictionary  = [[NSDictionary alloc]
                    initWithObjects:[NSArray arrayWithObjects:@"aString", @"anotherString", nil]
                            forKeys:[NSArray arrayWithObjects:@"aKey", @"anotherKey", nil]];