What is the difference between 'wann', 'wenn' and 'als', don't they all mean 'when'?

'wann' is only used as a question word. e.g. 'wann spielst du Fußball?' = 'when do you play football?''wenn' is used like 'if' and 'whenever' in English. This is the most common usage of the word and is used in the present and conditional. e.g. 'wenn ich in den Park gehe, spiele ich Fußball' = 'whenever i go to the park, i play football'or 'wenn ich reich sein würde, würde ich ein cooles Auto kaufen' = 'if I was rich, i would buy a cool car' 'als' replaces 'wenn' if you are speaking in the past tense; e.g. 'als ich Fußball im Park gespielt habe...' = 'when i played football in the park'