Deposition is the process by which a river/ocean deposits its load (typically stones and sand) somewhere.
A spit is formed where the line of the coast changes. Longshore drift moves sediment along the coast in the same direction but when the coastline changes direction, the sediment is deposited as a ridge. This ridge stretches away from the coastline forming a spit.
Constructive waves deposit material when they break on the shore in a sheltered bay as they run out of energy. The backwash is weak and so sand and pebbles are left behind to form a beach.
Destructive waves have a weak swash yet a stong backwash meaning that when they break and the water retreats, pebbles and sand are pulled back down the beach. Basically they destroy beaches by removing the material.
Longshore drift is the zig-zag movement of waves which causes the load of sediment the waves are carrying to build up and cause erosion.
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