The verb poder (to be able, can) is one of the 10 most common verbs in Spanish. This verb is irregular, which means that it's unique in its conjugations. Let's study some common expressions in which this verb is used.
Most of the time the verb poder functions as an auxiliary verb (just like its English counterparts "can" and "could"), but in Spanish poder is followed by an infinitive. In the present tense you could find it used to express the ability or permission to do something:
Hay mucho que tú puedes hacer.
There is a lot that you can do.
Caption 44, 3R - Campaña de reciclaje - Part 2
¿Yo puedo ir a tú casa?
Can I go to your house?
Caption 65, 75 minutos - Del campo a la mesa - Part 15
Compare this to the use of puedo with reflexive pronouns in the same video:
¿Yo me puedo apuntar a eso? -Claro.
Can I sign up for that? -Sure.
Caption 28, 75 minutos - Del campo a la mesa - Part 15
You can also use the reflexive pronoun as a suffix of the verb in the infinitive. So it's also correct to say puedo apuntarme (can I sign up). In Spanish the idea behind the use of reflexive here is that you write down your own name yourself. If you don't use the reflexive and only say puedo apuntar, then the expression means I can write down. For example: puedo apuntar tu nombre (I can write down your name).
The combination of the reflexive with the verb poder is also used to talk about abilities or possibilities in an impersonal way. For this you will always use the pronoun se, and the third-person of the verb. For example, se puede nadar (one can swim). Many Spanish speakers use an abbreviation of the impersonal expression ¿se puede pasar? (literally "may one come in?") as a courtesy before entering a house or a room:
¿Se puede? Sí. -Sí. -Soy Toñi. -Encantada.
May I? Yes. -Yes. -I'm Toñi. -Glad to meet you.
Caption 7, 75 minutos - Del campo a la mesa - Part 14
Of course, you can also not use the impersonal and say ¿puedo pasar? (May I come in?). The equivalent of the shortened expression "may I" is simply ¿puedo?, which, as in English, can be used to ask for permission to do something, not only entering a room.
Now, the combination of the verb poder with the reflexive se can also indicate the use of a special type of passive voice. In the following example, the doctor is talking about ozone:
Se puede obtener artificialmente a partir de descargas eléctricas.
It can be obtained artificially through electrical discharges.
Caption 28, Los médicos explican - Beneficios del ozono
FYI: the normal passive voice construction for this would be: puede ser obtenido (it can be obtained).
We will continue studying more expressions that use the verb poder with other tenses and moods in a future lesson. We leave you with a very common expression of disbelief or surprise that uses the verb poder: no puede ser (it can’t be). We even have a series titled NPS, an acronym of no puede ser. ¿Puedes creerlo? (can you believe it?)
¡No puede ser! -¡No puede ser!
It can't be! -It can't be.
Caption 52, NPS No puede ser - 1 - El concurso - Part 2