We have this thing we do in English, and we tend to follow it rather religiously. If we are in the middle of an action, we use what is called the present progressive tense (“I am studying”) to indicate that the action is unfinished and in process. It’s neat, it’s logical, it works. We do the same if we are speaking of an ongoing action in the past (“I was studying”); this is called the past progressive.
For example, if you were to ask, “What are you doing?” you would expect an answer likewise in the present progressive, like “I am going out.” After all, it would sound really silly to ask, instead, “What do you do?” and to get the answer “I go out.” It would, in fact, mean something else. The same is true of the question “What were you doing?” as opposed to “What did you do?” They are two different questions.
Unfortunately for us, Spanish speakers – indeed, speakers of Romance languages in general – don’t necessarily do what we see as the logical thing. In fact, to express the present, they tend to use the simple present tense most of the time. As a result, the question “¿Qué hace usted?” can technically mean “What are you doing?” or “What do you do?” (Although a native speaker would probably ask something like “¿En qué trabaja?” (In what do you work?) rather than “¿Qué hace?”)
And the past is no problem, because Spanish has the imperfect tense to take care of that: “¿Qué hacía?” (What were you doing?) as opposed to “¿Qué hizo?” (What did you do?).
It’s not that it’s wrong to use a progressive in Spanish; it’s just not what native speakers usually do. You will be perfectly understood, though you may sound a bit quaint, if you use the present progressive tense for an action in progress. I’ve been here forever, and I still do it once in a while. It’s difficult not to because it is so prevalent in English.
Another difference is that the present progressive in Spanish is never used to express the future, as it is in English.
Thus, “We are eating dinner at Mom’s house tonight” might be expressed as “Vamos a comer donde mami esta noche” or “Comeremos donde mami esta noche,” among others, but never “Estamos comiendo donde mami esta noche.”
Moreover, the present progressive is seldom used with common verbs of motion like ir (“to go”) and venir (“to come”); with verbs referring to mental states like amar (“to love”) and saber (“to know”); with the verbs estar, ser (both forms of “to be”) and poder (“to be able”); or with the verb llevar, when it means “to wear.”
There is a test, though not always reliable, that you can do to discover whether the present progressive will work with a determined verb. Simply add the phrase “in the process of” and see if it works. For example, “She is in the process of wearing a red dress” sounds silly, therefore llevar in the sense of “to wear” is not acceptable; whereas “She is in the process of eating” makes perfect sense. Keep in mind, however, that just because a verb can be used with a progressive tense does not mean it should be.
So when do native Spanish speakers use the present progressive? Usually it’s to emphasize or make clear that something is now in progress or is being repeated. For example: ¿Ha terminado su tarea Jorge? (Has Jorge finished his homework?) No, lo está terminando ahora. (No, he’s just now finishing it.)
In the end, the important thing to keep in mind is that the progressive is rarely used in Spanish and should be avoided unless you are sure that what you want to say really requires it.