Hola, "Brand new" significa "nuevecito" en el sentido de que algo acaba de ser creado o construido. "New" es nuevo, en el sentido de novedad, sin necesariamente ser algo recién creado o construido.

Something "brand new" is what we refer to when a product is new, and has never been touched or used by anyone before. Example: "My parents bought a house in East Ridge." "Oh, that area was just developed a few months ago, so they have a *brand new* house!" Something "new" could be something recently made (or modern), but that doesn't mean that it hasn't been used or touched by many people already. Example: "These *new* cars they make today aren't like the cars they used to make back in the 1960s!" 'New' also refers to something new to you, but it doesn't mean necessarily that it's a new product in general. Example: "I bought a *new* lamp for the house. It's an antique." (This means it's old, and likely had others using it before, but it's new to me.)

I searched this on Google's ngram viewer - see link. The page also returned "Ngrams not found: bought a brand new computer, bought a brand new house The Ngram Viewer is case sensitive. Check your capitalization!" This means that the entire google corpus - a huge and varied library of native English text - contains no examples of the phrases not found. https://books.google.com/ngrams/graph?content=bought+a+new+car%2Cbought+a+brand+new+car%2Cbought+a+new+computer%2Cbought+a+brand+new+computer%2C+bought+a+new+house%2C+bought+a+brand+new+house&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cbought%20a%20new%20car%3B%2Cc0%3B.t1%3B%2Cbought%20a%20brand%20new%20car%3B%2Cc0%3B.t1%3B%2Cbought%20a%20new%20computer%3B%2Cc0%3B.t1%3B%2Cbought%20a%20new%20house%3B%2Cc0

The term 'brand new' is commonly used as an exclamatory statement to express surprise, excitement or even disappointment. For example, if I buy something second-hand it has likely been used before and even more likely, it has been used a lot. But you might buy a book where the spine hasn't yet been cracked or clothes with tags still on them and you might exclaim to your friend you got these things second-hand but "they're brand new!" kind of with surprise and excitement. You could also say something is 'almost brand new' or 'like brand new' if you know it's been used a lot but shows no signs of wear, often as a way of expressing excitement over getting a good deal. On the other hand, if I have just bought a new shirt and am wearing it for the first time and spill something on it, I might get upset with myself and lament with disappointment to whoever is with me "this is brand new, how could I be so careless?!".

Brand new means that you are the first person to have owned it. You use to emphasize that you are the first owner because we can say new as in new to you. For example, I bought a new car can mean new to you or it can mean that you are the first owner. I bought a brand new car means your are the first owner Andres: I bought a new car. Your friend: Is it brand new? Andres: Yes! (means you are the first owner). Andres: I bought a new car. Your friend: Is it brand new? Andres: No. (means you bought it used but it is new to you). Of course some things are implied to be brand new, like toothbrush, food, etc. Just new is not really used much.