The Portuguese infinitive is just the verb itself – unconjugated. These generally translate as “to run, to drink, to love, to do” ETC.
ar verb » Eu não quero falar. I don't want to speak.
er verb » A gente vai ter uma festa. We're going to have a party.
ir verb » A que horas você vai partir? What time are you going to depart?
But the simple ‘to run’, ‘to get’ ETC translations get changed whenever preceded by words (prepositions) that are connecting things together in a sentence.
These are usually de, em, a, sem, para and até.
a = at, to Comecei a estudar português. Let's start to running.
de = of, from Acabei de comer. I'm going to stop drinking coffee.
em = in, on Ela insiste em falar inglês. I have difficulty saying no.
sem = without Estou falando sem parar. I'm talking non-stop.
até = until Ela vai comer até morrer. She's going to eat until death.
para = to, for Estudo para aprender. She's ready to travel.