Objective-C is the primary programming language you use when writing software for OS X and iOS. It's a superset of the C programming language and provides object-oriented capabilities and a dynamic runtime.
Objective-C inherits the syntax, primitive types, and flow control statements of C and adds syntax for defining classes and methods.
When building apps for iOS, you'll spend most of your time working with objects. Those objects are instances of Objective-C classes, some of which are provided for you by Cocoa Touch and some of which you'll write yourself.
An app is built as a large ecosystem of interconnected objects that communicate with each other to solve specific problems, such as displaying a visual interface, responding to user input, or storing information. For iOS development, you don't need to create objects from scratch to solve every conceivable problem; instead you have a large library of existing objects available for your use, provided by Cocoa Touch for iOS.