There are several options to start learning programming. I myself learned Java when I started programming in school, but that was in school. Java is a great language to begin with, because it's very similar to other programming languages, like C#.
Another option I know is popular is JavaScript. I personally wouldn't recommend this, because fixing errors is very time consuming, because JavaScript doesn't really give you the best errors. It is however a very easy language to start with, and it's very, very powerful (it is, however, the most misunderstood language, and I don't think many programmers specialize in JavaScript. However with the current move to HTML5, which JavaScript is a part of, it's getting much more popular.)
There are many concepts that you should learn when programming, but not all of them are as important. OOP (Object Orientated Programming) is the one thing you can't go without if you understand it, but when starting out, it's better to ignore it. In things like Java that's a bit harder, but with things like JavaScript that's very easy to do.
I'd start out with a few tutorials. There are many programming languages that you can work with on Mac OS X. I'd stay away from Apple's Objective-C, though, because that's quite advanced. Java is platform independant, as is JavaScript. Choosing the language is important, because then you can search for a few good tutorials. I like the totorials done by TheNewBoston on youtube, but you might like a text based tutorial. Find one that suits your style, but don't get too theoretical. Practical knowledge is important when starting out.