Do we need to inform school within 90 days of OPT period.. Need help guys.

 "within 90 days of OPT period"
what are you really trying to ask? are you asking if you're required to notify your school regarding your employment status after 3 months of your OPT start date? or are you talking about the 3 months before/after your OPT starts/expires respectively?
if you really need help like you wrote above, you should consider spending a little more time to explain your situation/question so that people can pitch in.  

 so far i believe, you wanted to ask if you ever have to inform your school about your status in and around 90th days of your OPT start date. If so, the answer is YES. It can be done in many ways depending on the school. Some school set up different login account to know if you are employed or not. However most school (usually international student office) send you an email asking what you are doing. So best thing to do is to keep checking your school email even though you graduated. If none of these things exist, then it's better to email coordinator/or officer telling what you are doing in about day 80. That would be fine.

trying to get information about notifying school regarding employment status after 3 months of OPT start date. I am not able to get any jobs right now. so what happens if i dont notify school. I have seen people staying in OPT for year doing nothing.  what are my options now.. 

different schools have different policies regarding reporting OPT status. in my case, the school requires me to report my employment status as soon as any change (like employer, post, etc) occurs and every 6 months, even if there's no change. your school's policy might be different from that of mine. check if there's any information about OPT reporting on your school's (international services office's, to be specific) website. if not, contact them and do as they say. often, school's are pretty flexible about the deadline for the reports, i did mine after about 8 months from my OPT start date and the school was fine with it.

keep on looking for a job. and depending on how good/bad your school is in helping international students, letting them (mainly your IS advisors) know about your situation and asking them for help to find a job might be an option. even better than that, contact all professors, mentors, internship program directors, etc you knew throughout college and ask if they (or someone they know) might be able to hook you up. 

and yeah, some people do spend whole year of their OPT doing nothing, but you don't want to be one of them, neither did they.

After I graduated (B.S.), I did not get job and what I did was contacted international student coordinator saying that "it had been 80 days of my OPT and I have not found the job but I am volunteering in one of the professor's lab". To be honest, I was not volunteering and the name of the professor that I gave them was my academic advisor during my undergrad. Then I got an email next day from the coordinator saying that he had reported my situation to the DHS (or something office) and I had OPT till one year. That's how things got solved. Time is tough these days to find job so I believe it won't be so hard to get extension after 90 days. Also I have not heard of anyone saying to have a problem beyond 90 days. Goodluck