Capillarity is the phenomenon through which water moves inside extremely thin tubes (capillaries) aided by the attraction between water molecules and the capillary wall. The capillarity phenomenon is possible because water is a polar molecule and forms intermolecular hydrogen bonds.
Therefore there is electrical attraction (adhesion force) between the capillary wall and the water molecules that then pull each other (cohesion force) since they are bound. Not just water but other liquids may move inside capillaries by capillarity.
Capillarity is not too relevant for the transport of water in plants. It contributes only to a few centimeters of ascension.