Este tiempo verbal se usa en los siguientes casos.

1. Acciones en progreso al momento de hablar. She is working now.
2. Acciones repetidas con los adverbios always. He is always helping people.
3. Hablar a cerca de planes futuros: We are playing tennis tomorrow.

Construcciòn del presente continuo

    I               am               playing           tennis
Sujeto        verbo              verbo          complemento
                   to be              + ing

     positive form                                     question form

        
Examples

¿ Is she wacthing tv right now?  Yes, she is  
¿ Is he playing tennis at the moment? No, he is not
¿ Are they listening to music now?  Yes, they are
¿ Are your friends dancing in a disco? No, they are not