Learn Portuguese (Portugal): Nós não compramos o carro neste stand, mas sim noutro. - We are not buying the car at this dealership, but rather at another one.

It is a contraction of the preposition em (in/at/on) and the masculine singular word outro (other/another). Because we are talking about buying a car at another dealership, we need the preposition em, which merges with outro to form noutro.

Why do we use mas sim here instead of just mas?

While mas simply means 'but', the phrase mas sim is used to strongly contradict a previous negative statement. Because the sentence starts by saying where we are not buying the car, we use mas sim to introduce the correct alternative. It translates well to 'but rather' or 'but instead'.

Why is the English word stand used in this sentence?

In Portugal, stand is a very common loanword used specifically to refer to a car dealership (often called um stand de automóveis). It is treated as a masculine noun, which is why we use neste (em + este) right before it.

The translation says 'at another one', but there is no word for 'one' in the Portuguese sentence. Why?

In Portuguese, you do not need a placeholder word like 'one' after words like outro. The word outro can stand perfectly on its own to mean 'another one', relying on the context (the dealership) to make sense.