im not able to understand the concepts of jee there is very less time left what to do ?

@ pramod 
donot distract at this point of time , thats the very imp thing . while attempting the exam every person have some strong part as well as some weak part . 

so, if u have not understood some chapter then taht will be your weak part , and also there will be some chap in which u are strong and u are sure that if any ques will come from their then u can surely answer that . 
then , strong those chapter and just read the besic formula of weak chapter so that if any easy ques will appear in jee , so, that u can solve it . 
but not ignore completely any chap , and make sure not to put the high weightage chap like complex number , mechanics , organic chemi in your weak part as they forms almost 50 percnt of jee papers . 
Now , u can have only study the besics , and start the attemption of mock test from december last week , 
as board mark has not been considered then dnt worry on that part , but at least 76 percent u required . 
ALL THE BEST ..