In Italian, to express an action that began in the past and is still going on in the present, use the verb in the present tense da length of time. This construction does not exist in English, where you would use the present perfect tense. Here are a few examples:
Leggo questo libro da una settimana. (I ve been reading this book for a week.)
Prendiamo lezioni di italiano da molti mesi. (We ve been taking Italian lessons for many months.)
To ask how long something has been going on, use da quanto tempo present-tense verb:
Da quanto tempo leggi questa rivista? (How long have you been reading this magazine?)
Leggo questa rivista da molto tempo. (I ve been reading this magazine for a long time.)