Acabar de, Volver a, Dejar de

These verb phrases put a conjugated verb before an infinitive or a gerund to show when or how something happens. The little word after the first verb is fixed:

• acabar de + infinitive = have just done: acabo de llegar (I've just arrived); in the past, acababa de (had just).
• volver a + infinitive = do again: volví a llamar (I called again).
• dejar de + infinitive = stop doing: dejó de fumar (he stopped smoking).
• empezar a + infinitive = start doing: empezó a llover (it started to rain).
• seguir + gerund, no preposition = still be doing: siguen jugando (they're still playing).
• llevar + time + gerund = have been doing for: llevo tres años estudiando.

Only the first verb changes. In parts of Latin America you will also hear tengo tres años estudiando.