To buy a dress in Engpsh, you can say "I want to buy a dress" or "I'm looking to purchase a dress." If you're looking for a specific type of dress, you can say "I want to buy a formal dress" or "I'm looking to purchase a summer dress." If you want to be more specific about the style or design of the dress, you can say "I want to buy a red, strapless dress" or "I'm looking to purchase a knee-length, A-pne dress."