i need to know the main difference between QPSK and 4QAM, i have searched over the internet and still i have not found a good explenation.
There are different types of QPSK: Offset (staggerd) QPSK, $\pi/4$-QPSK, etc.
In its most known form, QPSK is identical to $4$-QAM or $4$-PSK. That is, the same constellation can be referred to by different names. So there is no difference.
This constellation can be seen in the picture bellow (from Wikipedia)
Similarly, $2$-QAM is actually the same as BPSK, as is also pointed out here.