If he's starting totally green, there's plenty of You Tube videos teaching basic rhythm and note values, and other theory.
As far as a "easy metal beat", that's pretty open ended as well. There's blast beats for the thrash metal stuff, then there's all the 16th note double bass stuff.
Personally if he's totally new to stuff, I'd recommend he use something like Sony Acid. It's not anywhere near as powerful as Sonar, but it's great for beginners, and people who don't know anything about music theory. After you get used to that, it's easier to step into something like Sonar.
Another up and comer that's more of a real basic, beginner DAW is Stagelight from Open Labs. I think it's like 10 bucks, and you don't really have to have a lot of knowledge to create something basic.
Not to take away anything from Sonar, but I think most professional DAWs like sonar are hard to approach if you don't know anything about music, or music technology. Where stuff like Acid has on screen walk through tutorials.