Skating Foward, The skaters push off their skates like on the picture. There are also friction involved when skating. The blade on the skate rubbing against the ice has a friction, but because the surface of the blade that is in contact with ice is so small, the friction is also very little. When the skater is skating foward, They usually only have the skate that they are pushing off the ice, on the ice, and the other skate is not in contact with the ice.
When going
backward, the skater has both of this skates on the ice, and is
transfering weight between the two skates, which helps him move
backwards. There are more friction when going backwards, because
both of the skates are touching the ice, which means more surface is in
contact with the ice, causing more friction than going foward.