hi Adam,
The recurrence is a repeating task, either based on a set frequency, once per week etc or by completion then x weeks after completed.
the review settings is a way to 'prioritise' your review process (GTD weekly review for example), i.e. how often you focus on a a particular branch and reconsider if its relevant given the current situation, or has a higher priority etc etc
Hope that helps, sorry not much time to put a detailed response down.