@ minu priya : m sorry but i think you mis-typed it,
instead of the highest freq component u wrote sampling freq
component .. so the real thing is that " whenever a signal
is being sampled, the sampling frequency has to be greater
than the highest frequency component of the message signal
to avoid any loss of information during sampling process" if
this condition is not satisfied, it leads to certain loss of
information. this condition, i.e ( Fs >= 2Fm ) is called the
nyquist rate.

Sampling theorem means,The sampling rate of the sampled
signal should be >= to Nyquist rate.Where Nyquist rate means
twice of the max of signal frequency .We can reconstruct the
original signal from the samples at the receiver end only
when the condition(Above) is met.
EX:Let the signal,that u want to sample, max frequency is 20kHZ.
Then Nyquist rate is 2*20kHZ=40kHZ.

Then the sampling rate is >=40kHZ.But generally sampling
rate units are mentioned as "Samples per Sec(Samples/sec)".
So for above example sampling rate is 40,000 samples/sec,if
sampling rate is equal to Nyquist rate.

Sampling theorem defined as sampling freq rate must double or equal to the signal freq to get orginal signal it is given by fs is equal to or twice of f.

samplin theorem says that a continous time signal may be
completely in its samples and recovered back if the samplig
frequency is fs>=2fm. here fs is the sampling frequency and
fm is the maximum frequency present in the signal

Sampling is the process of converting a signal from analog to digital in frequency domain.. the signal should satisfies the nyquist condition., I.e., fs is greater than or equal to 2fm..

sampling theorem only for band limited signals only.
Sampling theorem
A bandlimited signal can be reconstructed exactly if it is
sampled at a rate atleast twice the maximum frequency
component in it.