should I always end a essay with a conclusion or it is ok with no conlusion at the end of a essay?
Well, aleaf, when you write an essay, you write it for a reason. Perhaps, you find the subject interesting, perhaps it's a matter you can relate to [we exclude the "it's-a-test" option here]. The point is, you want to transmit a message and the best way to do that is to maintain a classical essay structure. I think a conclusion is very important. If you've seen "The King's Speech", perhaps you remember that last radio broadcast about the beginning of WW1. And it's ending, the conclusion, was the most powerful part of the king's (um) essay. :)
Secondly, how to write an article with more profoundly when there is a word-limitation there? I have refered to other related essays on line and I found that I have a difficulty expressing myself with short and precise sentences. Would you give me some advice to that issue?
Oh, I have problems with word limit too! What I personally try to do is focus on quality, not quantity. So, I mention the most important aspects I must take into consideration and -if there's any room left- I add the most relevant details. There's really no other option here than really trimming your ideas down to the core.
However, if it's not a serious essay you can, of course, just play around with words. :D
My Romanian teacher gave me some great advice last year: "A good writer keeps things simple." And most of the times honestly, simplicity can be your best ally.