If a user asks to check essay, are we allowed to do that or is that off-topic. I'm a little confused regarding that.
Simply "Please check my essay" is off-topic and has been for a very long time. The reason is principally that it only helps one person: Stack Exchange seeks to be a repository of knowledge in Q&A form which will help others in the future.
If we were to check/correct an essay, it's quite likely that we would be assisting in completing some examination or test, which should be one person's sole work. It would be assisting in cheating. There are cases where that won't apply, but attempting to differentiate is Too Difficult, so there is a blanket ban.
An entire essay is (as Mitch has commented) "way too much work". Have a look round at some highly-voted answers on the site, and the amount of work which can be put into answering a seemingly simple, innocuous question. Scale that up to an essay. Which parts of the essay should get that treatment?
It is possible to apply a level of detail to a specific point within an essay. The asker should choose a single aspect of a single sentence and ask a well-formed question about that. (Which indicates another issue with text-checking: generally it shows that the asker is lazy and can't be bothered to do any analysis of their own work. That doesn't go down well, as a rule.)
Checking texts is explicitly mentioned in the Help pages, which explain that proof-reading is explicitly off-topic, and show how an acceptable question might be formulated.
How can I ask about checking my text?
Checking a text is proof-reading. This site does not offer a proof-reading service where the community will read a text and suggest corrections. If you would like that, there are online services available, a few of which are free.
However, this site can answer specific questions about a particular point in your text. You need to quote the passage, highlight the word you're uncertain about, and then explain why you're not sure about it.
That is, not
Is the verb right in "He has run the company for five years now"?
but something like
He has run the company for five years now.
Is the verb has run correct here? If "he" is still in post, the action is still in progress, so should the verb be a continuous/progressive verb like He has been running? Does the inclusion of "now" make a difference here?
- The question "Is the verb has run correct here?" highlights what the question is asking about.
- "The action is still in progress, so should it be a continuous-aspect verb?" explains the quandary.
- "Does now make a difference?" provides additional information about the question which answers might touch upon.
Note that you should also include your own research into the query. The example indicates that a little research may have been done with "Should it be a continuous-aspect verb?", but research is needed.
Don't forget to tag the question with tags which are relevant to the particular points you're asking about: [verbs][progressive-aspect] would be a reasonable choice in this example.