Deposition is a process in which rocks, soil, and sediments are transported and added to a certain location to form a landmass. The deposits can be carried via "wind, water, or ice" ("Deposition of Sediment"). Deposition in rivers, oceans, and glaciers certainly can form a number of different landmasses. As we are limited in space, below is a few ideas and sources to help get you started.
In rivers, deposition can occur with respect to bends in the river. The flow of water can be very fast outside of river bends but slow inside of bends. As the water moves slow enough, the debris picked up by the currents are deposited along the banks inside of the bends. Other deposition can take place when a river floods after a heavy rain. As the water spreads out over the floodplain, the water barely moves, also allowing the debris to be deposited on the floodplain. As sediment deposition builds up over time, it can create deltas at the mouth of rivers. Delta's are landmasses at the mouths of rivers that have been built up by the sediment collections. The most famous and largest deltas are the Mississippi River Delta and the Nile River Delta ("Rivers & Deltas").
Similarly, as ocean waves carry sediment, the currents deposit the sediment near land, creating beaches. The beaches created by waves are sandy and have ripple-marks. Aside from beaches, sediment can again become so built up due to deposition that the sediment creates sand banks, which can be created near the sea shore and even across river mouths that open into the ocean. Such sand banks partially enclose the water of the ocean meeting the water flowing into the ocean from the mouths of rivers, and we call these enclosures estuaries. Hence, another effect of deposition in oceans is the creation of sand banks, which in turn creates estuaries. The build up of sediment that creates sand banks can also create tidal flats ("Shoreline & Near-shore Environments"). Deposition in oceans can even create reefs. Reefs mostly form in shallow waters when the waves deposit "skeletons of organisms," like corals, creating "wave-resistant, rocky structures" ("Shoreline"). Both sand bars built up away from the shore and coral reefs can also form lagoons, which are shallow, sheltered areas of the sea ("Shoreline"). Hence, deposition due to ocean waves can create beaches, sand bars, and coral reefs, and those sand bars and coral reefs can in turn create estuaries and lagoons.
One of the most common features caused by deposition is river deltas. These are the result of rivers depositing sediment in a fan-like pattern where they meet the ocean.
Glaciers often carve out valleys as they inch along. But, unlike regular mountain valleys, these tend to have a rounded out U shape as oposed to a sharp V shape. Glaciers also leave behind bits of sediment and rock. Rocks and stones left by glaciers are called eratics.