1. As a noun, sometimes preceded by “el”, the masculine singular form of the definite article. Note here the use of the -ing form in English for the Spanish infinitive.
Entre las recomendaciones está el mantener… (Among the recommendations is maintaining…)
2. After prepositions and prepositional phrases.
Antes de iniciar un plan… (Before starting a programme…)
Para aprender… (In order to learn…)
3. After modal verbs such as poder to be able, can, may, deber must, tener que to have to…
Debe ser de entre 20 y 30 minutos… (It must be between 20 and 30 minutes…)
4. After a number of verbs, some of which may require a preposition.
Nos ayudarán a determinar… (They’ll allow us to determinate…)
Jamás la he oído cantar. (I’ve never heard her sing.)
5. Preceded by “al”, usually expressed in English with on + ing.
Al comenzar un programa… (On starting a programme…)