With respect to interrupts what is the importance of:
1. Interrupt flags
2. Context saving

what is the meaning of the instruction ' Rlf or just rotate, what does it do?

 

When an interrupt occurs, how are you going to tell what caused the interrupt?

Have a look at this page:
http://tutor.al-williams.com/pic-inst.html

 

Interrupt flags are for setting which conditions cause an interrupt and also telling you which one has happened.
Context saving is so that if the code in the interrupt affects W and STATUS that they will be restored after the interrupt.

All the bits just move one to the left through carry. You can use it to multiply or divide by powers of 2.