This is a mish mash of every street market you've ever seen! They sell old and new clothes, fresh fruit and vegetable, antiques, puppies and birds, books, music, artisan wares, jewelry, old suitcases, electrical appliances that haven't worked in years and everything in between!
If you want a taste of street markets in Montevideo then check out this wonderful video of the Tristan Narvaja Market.
Link: Feria de Tristan Narvaja (mercado de "pulgas") - Monte