OR vs XOR gateway

Yes, shrutij.

Very simply:

Do you want all flows that apply to this instance to happen simultaneously in parallel, or do you want the process to continue as soon as any merging flows arrive at this point? OR gateway

Do you want multiple parallel flows to begin at this point with no restrictions, or do you want the process to wait here until all incoming merging flows reach this point (wait until parallel processes are all done)? AND gateway

Do you want one and only one process flow to move forward and make a mutually exclusive decision about the only path the flow should take from here? XOR gateway (Yes you almost always use this one. You could go months or years without ever using the others)

Do you have to manage multiple incoming and outgoing flows at the same time using the same gateway? COMPLEX gateway

OR All cases that evaluate true result in a process flow, at minimum none, at most all of them.

XOR Only the first condition that evaluates true will be selected and move forward.