These indicative sentences are interesting, given that they are in the Requests 1 skill.
If this is a request in the indicative, then it should not be translated as you are closing the door. Rather, with emphasis, you close the door.
At least that is how I understand the indicative used as a command.
I think ... the second person (tu) is being used in Requests 1 to make a point. You can use a 3rd person verb to make a simple request - but not a second person. "Tu cierras la puerta" is not a request to close the door. But "Cierra la puerta" has two meanings, one of which is: "Close the door". I am still learning, but I think this is right.
You are right. Translation is "You close the door". The answer doulingo gives is " Tu estas cierrando la puerta". I encountered a lot of answer in this form.
Duo's goal is that sentences can be translated into whatever is valid out of context, and since the given sentence is just a normal indicative, "You are closing the door" is fine here.
Is it wrong to say, tu estas cierrando la puerta? If not, how is it said most of the time?
It's not exactly wrong to say it, but it's a very weird sentence. To use the present progressive in Spanish, the action must be in progress at the moment of speech, and you commenting on someone closing the door right now is kinda odd.
The simple tenses are used most often in Spanish. Progressives are only used where it really matters.
Also please note that the gerundio of cerrar is cerrando. No 'i'.
Now is you are closing the door. It is equal to the previous one! So why this one is right and the other was wrong
Because there's no question mark in the sentence. Having said that, it is an odd sentence. It works as a phrase though e.g. When you have made sure everyone's left, you close the door.