"This dress is very simple."
Translation:Este vestido es muy simple.
esto = this (pronoun). There is no noun after esto since it's a pronoun. It's used to refer to a genderless situation/action/event... For instance ¿Has visto esto? = Have you seen this? or Esto es fácil = This is easy.
The word estes doesn't exist in Spanish, so I guess you meant este. Well este = this (determiner) or this one (pronoun). It's a determiner when it's followed by a masculine noun, for instance Este vestido = This dress. It's a pronoun when it's not followed by a noun, and it refers to a masculine noun. For instance ¡Mira los vestidos! Este es rojo. = Look at the dresses! This one is red. In this case, it's also common to write it éste