Before we can talk about the details of Objective-C, we need to acknowledge its history. Objective-C is based on a language called simply "C". The C programming language was one of the first highly portable languages. Portable means that the same C code could be compiled to run on any processor as long as someone writes a compiler for that platform. Before that, most of the code was written in Assembly; which always had to be written specifically for each processor it would run on.
C is what is commonly referred to as a procedural programming language. It is built on the concept of a series of functions that call each other. It has a very basic support to create your own types, but it has no built in concept of objects. Objective-C was developed as an object-oriented extension to C. Just as Swift is backwards compatible with Objective-C, Objective-C is backwards compatible with C. Really, it simply adds object-oriented features on top of C with some new syntax and...