The form you already know
estar + gerund is the Spanish present progressive: a form of to be plus an -ing form, as in I am eating. Building it is easy; the harder part is that Spanish uses it much less than English.
Only estar changes with the person (estoy, estás, está ...); the gerund never moves: estoy hablando, estamos hablando. English am covers both Spanish to be verbs, but here only estar works. The gerund ends in -ando for -ar verbs (hablando) and -iendo for -er and -ir verbs (comiendo, viviendo).
Estoy comiendo.
I'm eating.
¿Qué estás haciendo?
What are you doing?
What it is for
Right now: something is happening at this very moment.
Ana está hablando por teléfono.
Ana is on the phone.
Está lloviendo mucho.
It's raining hard.
A limited period: something is true now, but not forever.
Estoy aprendiendo español.
I'm learning Spanish.
Este mes estoy trabajando en Madrid.
This month I'm working in Madrid.
The habit you have to break
English reaches for the progressive almost automatically. Spanish does not. For habits, general statements and the future it takes the plain present. Where English says I am doing, Spanish often just says hago.
Leo muchos libros.
I read a lot of books.
Cenamos a las ocho.
We have dinner at eight.
Negation and pronouns
no goes before estar. Pronouns go before estar or attach to the gerund, then with an accent. English keeps the pronoun after the verb (I'm doing it), which Spanish does not.
No estoy trabajando.
I'm not working.
Lo estoy haciendo.
I'm doing it.
Estoy haciéndolo.
I'm doing it.
