What is input capacitance of pins in IC and what effect does it have?
The input capacitance is the capacitance a signal source sees, when you connect the source to that IC pin. This means, if you apply a logic HIGH to that input pin your source has to supply sufficient charge to charge up the capacitance to the desired voltage level.  
It might be measured directly with something like an LCR meter at the produced item or it might even be just a calculation from the design layout of the chip.
Depending on your source impedance it takes time to charge up the input to a specific voltage level. If you know the source impedance as well as the input capacitance you can calculate the exact behaviour of transient events.