To a foundation: start with an ace, then build up in the same suit — A, 2, 3 and so on to king.; Within the tableau: build down in alternating colours — a red six onto a black seven.; A face-up run may be moved as a unit if the sequence stays valid.
Why people argue about this
People often assume that you can only move face-up runs as a unit if they stay within the same suit, forgetting that the key part is keeping the sequence valid across different suits too — so moving a red six over to a black seven in the tableau isn't allowed just because it's a run.
