I mostly agree except it is good to draw a line between allowing constant repeated beginner questions (like you get in the SO PHP tag) and attracting quality content and empowering and enabling research of the sites content, or even of the greater internet when something seems extremely base and highly repeated or too easy.
Remember we are not essentially tutors, robbing those who teach Arabic of a job. We are instead a community of individuals who possess one thing in common: an interest in the study and comprehension of the Arabic language.
Can we ask to explain the grammar of a sentence?
Yes, these rules are essential and by no means simple, even if the rule you are asking about is the most simplest of all. Arabic is a very complicated language compared to many Latin languages (i.e. English) so, yes, definitely on topic.
Can we ask questions like how do you say X in Arabic?
I would normally say no. We are not a translation service. If you need something that complete translating then I would recommend you seek either a translator or an Arabic course.
can we ask meaning of an Arabic word?
Again this is one which normally draws low quality posts, i.e. what is the meaning of kalbun?
However, there are some questions that can be very interesting when asking about the meaning of a word. However, those topics are not normally basic and are for more advanced, if not scholar-type individuals normally.
However, that being said, if Google (etc) Translate is simply not good enough (which is isn't for quite a few words) then your question could be answered here since it clearly has got no equal else where on the internet.
So it is really a case of: What questions do you need answering?
The community will then judge to see if they are fit for the site.