Difference between OFDM and FDM In Frequency Division Multiplexing we provide one channel to one user.

Example like BandWidth of user1's voice is 200Khz. I provide one channel of 200KHz in FDM for uplink as shown in the figure. 
Now I will provide another 200KHz Bandwidth(channel 2) for user2's voice. Similarly for user3.
I will be having a guard band of 100 Hz for this. 

Now What I understand about OFDM is that channel1 will be orthogonal to all other channels. Also, we divide channel 1 into orthogonal sub-carriers with bandwidth less than 200KHz.
Am I correct? If yes then will there be no ISI as my required Bandwidth is 200KHz.
Both are orthogonal in your example, in different ways. The FDM example provides orthogonality by properly spacing the signals in the frequency domain (their dot product is 0). OFDM is far more spectrally efficient where you have overlapping carriers that are orthogonal. 

From an implementation standpoint OFDM can be achieved with a DFT. Each of the carriers is a much lower bit rate that turns a frequency selective fading channel into flat fading. This is not true for your FDM example. There are many other differences but these are a few.