Hello elsongs,
I agree with you! It's always a good thing to know more than one platform.
Here's how the update process works. We are currently on OS X 10.7.2. 10.7.3 could be coming out at anytime in between a week and a month. All the 10.7.x updates are FREE! All you do is just click on the apple logo in the upper left hand corner and click on Software Update.
Now when 10.8 comes out, you will need to purchase it. It'll be a digital download most likely from the Mac App Store. You'll buy it there and it downloads an installer file. You'll click on it and then just follow the instructions. It's always a good idea to backup your system for major OS updates. But I've gone through 3 major OS X updates (10.4, 10.5, 10.6, and 10.7) and I've never had a problem!
I hope this answers your question.
Welcome to the Mac community

Hope you love it!
Cheers
Searay