The Cokin Gradual ND Kit plus Holder (H3H0-25) contains: the ND2 filter (P121L) with 1 stop density and hard edged transition; the ND4 filter (P121M) with 2 stop density and hard edged transition; and the ND8 filter (P121S) with 3 stop density and soft edged transition.
Also included in this kit is a P-series filter holder (measuring 84x84mm), meaning that the only extra thing you'll need to get started is an adapter ring, the diameter of which will depend on which lens you are using.