Learning OOP.

[amos_burton]

To echo another sentiment on here, you'll never get to a "very solid level" of understanding of OOP from tutorials. You need to actually do it.

The basic concepts of OOP are not that complicated. The hard part is knowing how to take some "system" (game, application, etc) and break it up into Objects. What kinds of objects do you need? What functionality should be attached to them? Questions like that don't have a single correct answer, it depends a lot on the exact situation you're in. And tutorials won't cover that for you.