can anyone tell me what is a proper sentence
A proper sentence is a complete one -- no fragments, no runons!
Proper sentences can range from one or two words to many, many words.
Go!
He's late.
...
In celebration of the International Year of Astronomy, a team of astronomers has developed an inexpensive telescope, which you assemble yourself, that magnifies objects 25 to 50 times, giving you the same view Galileo had 400 years ago.
(from http://blogs.chron.com/sciguy )
A sentence includes a subject and a verb, a capital letter at the beginning and correct punctuation at the end, and it makes sense on its own.
http://grammar.ccc.commnet.edu/grammar/sentences.htm