How?
In 1990, five shipping containers of sneakers and boots fell into the ocean and were lost to a Pacific storm. Then, another tragedy with rubber duckies and other bath toys in 1992. All those bathing items floated to the shoes. Last, in 1994 a ship lost 34,000 pieces of hockey gear to the sea. All the trash floated together creating the garbage patch. The currents carrying trash will stop and dump it all off.
What the trash affects is the animals. Like this sea turtle that is in the background, when the animal was little it got stuck in the plastic and as it got older and wider the stomach stayed the same size as the rest of the body got bigger. This turtle probably has stomach problems because the intestines are getting smooshed by the plastic.