Question

How I must remove objects?
For example, I have NSDictionary and some NSStrings from it:

NSDictionary *dict = [NSDictionary dictionaryWithObjects....];
NSString *str = [dict objectForKey:@"key"];

[str release]; or [str dealloc]; or str = nil or it’s autorelease object?

If I will remove not autorelease dict, will all child removed too?

Answer 1

Memory management in objective c is based on object ownership. If you own the object you must release that object.
Cocoa sets the following policy:

You own any object you create
You create an object using a method whose name begins with “alloc”, “new”, “copy”, or “mutableCopy” (for example, alloc, newObject, or mutableCopy).

You can take ownership of an object using retain.

When you no longer need it, you must relinquish ownership of an object you own
You relinquish ownership of an object by sending it a release message or an autorelease message.

You must not relinquish ownership of an object you do not own

This is just corollary of the previous policy rules, stated explicitly.
In your case

NSDictionary *dict = [NSDictionary dictionaryWithObjects....];
NSString *str = [dict objectForKey:@"key"];  

you are not owner of str, so you should not release that object.