Present progressive

English says 'I'm flying to Madrid tomorrow'. Translate that word for word and you get wrong Spanish, because estar plus gerund describes only what is already under way. For a planned future use the plain present, or ir a plus infinitive. Rule of thumb: if the action has not started, the progressive is wrong.

To say how long something has been going on, Spanish uses llevar plus a time plus a gerund, and it keeps llevar in the present because the action still is. Llevo dos horas estudiando. Llevamos un año viviendo aquí. English switches to a perfect at this point and Spanish does not, which is why the clumsy 'have been -ing for' calque gives you away.

Drop the infinitive ending and add -ando to -ar verbs and -iendo to -er and -ir verbs: hablando, comiendo, viviendo. After a vowel the i is written y: leyendo, oyendo. Stem-changing -ir verbs change e to i or o to u: pidiendo, durmiendo. Only estar changes for the person.

With estar plus a gerund, an object pronoun goes before estar or joins the end of the gerund, and both mean the same. Joined on, the gerund needs a written accent to keep its stress: haciéndolo, esperándome. It never goes between the two: está me esperando is wrong.