Estoy leyendo un libro interesante.
English: I am reading an interesting book.
The 'gerundio' and 'participio' are verb forms in Spanish used in complex structures to show ongoing actions or completed actions, often combined with other verbs.
Use the gerundio to show an action happening at the same time as another, or to describe how something is done. Use the participio to show a completed action, often with 'haber' or as an adjective.
Estoy leyendo un libro interesante.
English: I am reading an interesting book.
He terminado el trabajo.
English: I have finished the work.
Salió corriendo de la casa.
English: He/She left the house running.
La puerta está cerrada.
English: The door is closed.