This is the 384th most frequent Spanish word.
primero
First.
Here, 'primero' is used as an adverb to mean 'first' or 'as the first step' in a sequence of actions.
Primero, necesitas mirar ambos lados de la calle antes de cruzar.
First, you need to look both ways of the street before crossing.
Here, 'primero' is used again as an adverb to indicate that the subject was the first to arrive.
Llegamos primero al lugar de la reunión.
We arrived first at the meeting location.
In this sentence, 'primer' (a form of 'primero') acts as an adjective modifying 'paso,' meaning 'the first' in a sequence.