poder

"To be able to" / "can" — a stem-changing modal verb (o→ue: puedo, puedes, puede), always followed directly by an infinitive with no preposition. Puedo asks about ability or permission; the conditional podría softens a request.

• ¿Puedo ayudarte? — Can I help you?
• No puedo venir mañana. — I can't come tomorrow.
• ¿Podrías repetir eso? — Could you repeat that?

Confusing poder (ability/permission — "I can because I'm able to or allowed to") with saber (learned skill — "I know how to"). "I can swim" because you know how is sé nadar, not puedo nadar.

Often confused with saber.

• politics "Sí, se puede" — Coined in 1972 by labor organizer Dolores Huerta during César Chávez's 25-day fast in Phoenix, Arizona — it became the rallying cry of the United Farm Workers. Barack Obama later credited it as the source of his 2008 campaign slogan "Yes we can."
• expression "Querer es poder" — A Spanish proverb meaning roughly "where there's a will, there's a way" — listed in the Instituto Cervantes's Refranero Multilingüe as an aphorism affirming that determination is what makes a goal achievable.