What is meaning of...

My Japanese language teacher often use this phrase お疲れ様 です。It has many meanings. I want to know meaning and when to use this phrase and can i use with superiors (目上 の 人)

"O-tsukare sama desu" is a standing phrase used often in business/company environment, roughly meaning "Thank you for your work," but quite often used as a greeting/acknowledgement (to start off a conversation, or in passing) among colleagues. I wonder if your language teacher ever explained how it is used?

It is not to be used for your superiors; you cannot use it as just as an greeting/acknowledgement to your superiors.
If you want to convey the sense of "Thank you for your work" at the end of the day, you should say お疲れが出ませんように (Best wishes that you don't tire from your work).

Having said this, I am sure that some would say oh that last sentence is too old-fashioned, etc. :)

Are you trying to ask if you can use it to your teacher?

Metioned alreday a lot use google search again. (not translate page)
http://lang-8.com/224608/journals/823887
https://en.wiktionary.org/w/index.php?title=%E3%81%8A%E7%96%B2%E3%82%8...

If using for same age/level/class or younger
no need "sama(様)" and "desu(です)/deshita(でした)"
= only "Otsukare!(おつかれ！) "enough.
More frank Otsukare'(おつかれっ！) or only Otsu!(おつ！)
or Ottsuu!(おっつー！) in younger/teens using a lot.

So this "otsukare(o+tsukare)" meaning important soul as Japanese
"気遣い(kizukai)" and "思いやり(omoiyari)" based.
http://ejje.weblio.jp/content/%E6%B0%97%E9%81%A3%E3%81%84
Most Japanese have "道徳心'(doutoku-shin)" based Buddhist customs.
http://ejje.weblio.jp/content/%E9%81%93%E5%BE%B3%E5%BF%83
https://ja.wikipedia.org/wiki/%E9%81%93%E5%BE%B3%E6%95%99%E8%82%B2

(extra)
Otsu! for writing same sound but different meaning Kanji "乙" instead a lot
from internet slang from 2ch (largest BBS in Japan).
http://lang-8.com/401772/journals/1501668
But this 乙 often for using as 皮肉(hiniku).
http://ejje.weblio.jp/content/%E7%9A%AE%E8%82%89

net slang :
https://ja.wikipedia.org/w/index.php?title=%E3%82%A4%E3%83%B3%E3%82%BF...

お疲れ様です is a typical greeting in business environment which mean "You worked very hard (therefore)you must be tired", some one cares about your work and participation but it refer to "Good day" "Hello" and "Good bye"(as leave work). It can be used various places especially in business field so it's a common and popular greeting. I actually don't like this greeting so much.

You can say お疲れ様です to 目上の人.