Срезать describes your action, when you cut something growing, for examples срезать розу. Нарезать means: you cut something in many small pieces: нарезать колбасу. Вырезать describes cutting smaller thing from a big one: often from a sheet of paper: вырезать квадрат. Порезать means often situation of injury: порезать палец. Разрезать we use when a big thing must be cut to a couple of smaller part: разрезать лист бумаги. Обрезать means cutting something along edges: обрезать углы. I hope I could explain this for you. :-)