does any body over here know after how long being here in US we can be abke apply for the green card and after how much time citizenship and how much time it will take to get the citizenship once we applied.

If you meet the requirement under any of the categories (family based, employment based, asylum etc.) you can apply anytime. Otherwise, I haven't seen any law that allows automatic adjustment of status to permanent resident because someone stayed here for 5 yrs or 10 yrs or 20 years. Once you get PR status, you can apply for citizenship after five years. Again, there are certain requirements including a civic test that you must pass to be a citizen of US.

thx for ur reply. do u know how much time it will take to get the citizenship once we apply

This ofcourse will depend on where have you applied. Typically, places where there are more influx of immigrants, hence more applicants, takes more time. Places like New York, LA, Dallas are running anywhere from a year to 18 months. If you are in places like Nebraska it could be as soon as six months.
Answer to your first question, you have to be Permanent resident for at least 5 yrs to be eligible for naturalization. The exception to this rule is that, if you have applied for PR through marriage to US citizen and you are still married to same person, than you are eligible for naturalization after 3 yrs. If you are applying in 5 yrs category, you are eligible to apply 90 days prior to your 5th anniversary of your Permanent Residency. I hope this has been helpful to you.

Mr. Lobo, thanks for the precise answer. I hope you are another philanthropic out to help countrymen in need.

thx for ur help