Learn Spanish (Spain): El coche azul es el primero.

In English, we often add the word "one" (like "the first one") so we don't have to repeat the noun. In Spanish, you do this by putting the definite article (el, la, los, or las) right before the ordinal number. Since coche is masculine and singular, we use el primero.

I've seen primer used for "first". Why is it primero here?

The number primero only drops its final -o (becoming primer) when it comes directly in front of a masculine singular noun, like in the phrase el primer coche. In this sentence, the word stands on its own as a pronoun at the end of the sentence, so it keeps the -o.

If we were talking about a feminine vehicle like la furgoneta (the van), would primero change?

Yes. Ordinal numbers work like adjectives and must match the gender and number of the noun they describe. If we were talking about a van, the sentence would become La furgoneta azul es la primera.

Why do we use es instead of está for a position in a line?

You might think of a car's position in a line or a race as a temporary state (which normally requires estar). However, when you are ranking things or identifying which item is first, second, or third, Spanish uses ser (here, es). You are defining its identity in the sequence, not its physical location.