You can specify laravel version when you're downloading using composer composer create-project laravel/framework application_name 4.2.17

Either way when learning Laravel 4 or 5, I guess a good video tutorial would be laracast's Laravel from Scratch series.

When installing laravel by default composer is going to get the latest which is 5.0. As pointed out by alenn88 in his answer you can specify the Laravel version in composer.

Keeping track of changes I guess check the Release Notes on Laravel Docs

Id learn 5. There's no point in learning 4 now as it is outdated. Laracasts is a great resource, although most of the videos require a paid subscription. I dont like books for things like this because by the time they get written and published, the next version of the technology is ready for release.

I think the best way to learn is to jump right in and do it. Pick a project and make it happen. Your code will be messy, unorganized, and painful to look at, but you will learn a great deal while making it. Think about it this way: everything you need to know is actually in the Laravel documentation. Its just sitting there waiting for you. You dont need a book or a video tutorial or anything else. As you stumble through your first application, you will run into all sorts of issues and when you do, you can find the solutions to your problems in the documentation. Dont sit around waiting for the perfect tutorial or book or whatever because it doesnt exist. Build something, even if it sucks.