The infinitive form of a verb is considered its “neutral” form. In English, it is preceded by ‘to’: to walk, to jump, etc. In Spanish, it ALWAYS ends in either -ar, -er or -ir: ‘amar’, ‘correr’, ‘vivir’. It is used to refer to the action itself, without placing it in a time period nor saying who performs it. As such, it often behaves as a noun: ‘escribir es fácil’ = ‘writing is easy’.