The 2 - 7 ranking system values hands in exactly the opposite way to the regular 5 card high system. Straights and flushes count against the hand. Aces always play high. This means that A, 2, 3, 4, 5 is not a straight but the lowest ace high hand. Also, A, 2, 3, 4, 5 suited is not a straight flush but instead the lowest ace high flush. High card hands are strong and are compared using the highest card first and working down.
Nuts. The best possible hand is 2, 3, 4, 5, 7 not of the same suit.