We've added the keyword "simple" to tasks which are limited in scope and don't require knowledge of a large portion of the code base. Thus they're good starting points to get you into development quickly. (Don't be afraid to try your hand at some other task if you think you have the required skills, these are just our recommendations and thus you might have skills which make other tasks easier to complete.)
Note that though the tasks doesn't require you to be familiar with all the code they might still require you to have good skills in other areas like OpenGL. And it's of course not a bad thing if you've gotten yourself familiar with a larger portion of the code base, it's just not required to be able to complete the task.