Many French verbs require a specific preposition — à or de — before an infinitive that follows them, and there's no reliable way to predict which one just from the English translation. Commencer à (to start to), aider à (to help to), and réussir à (to succeed in) all take à: j'apprends à nager (I'm learning to swim).
Décider de (to decide to), essayer de (to try to), and finir de (to finish) all take de: j'essaie de comprendre (I'm trying to understand). Because English often uses the same "to" construction regardless, these have to be learned verb by verb, ideally by memorizing each new verb together with its preposition.