Answer:
Striations are "scratches" left in bedrock by glaciers. A small particle of rock, generally pebble sized or smaller, becomes entrained in the base of the glacier and dragged along the surface of the bedrock. These can often be seen on hard bedrock surfaces that are resistant to subsequent weathering after the retreat of the glacier.
Erratics are large rocks that are found out of place in the landscape, i.e. not near where they were formed. They are removed from their provenance by a glacier and transported away, before being deposited in a different part or the landscape when the glacier melts.