In broad terms RNA interference refers to the process of silencing mRNA. It is done by producing a complementary strand of mRNA to which the mRNA binds and forms double stranded RNA. The ds form of RNA makes it inactive and therefore RNA is unable to perform its function.
The process is well explained at the link https://www.meritnation.com/study-online/study-material/8MFLE3k8W5AinaSdZ$wYbg!!/OFta@pzvqntdrAAAu66Neg!! in the study material.
In simple words, interference is the addition of two or more waves meet at point that results in a new wave pattern.
When two or more waves are passing through a medium, the net displacement of the wave is given by vector sum of the displacement caused by all the waves. The principle of taking vector sum is known as superposition of waves. It can be both constructive and destructive.
The points at which waves arrive in phase (phase difference = 0), maximum displacement is observed which is called constructive interference. When the two waves arrive at a point such that they are out of phase (phase difference = π), minimum displacement is observed, which is called destructive interference.
Interference is the phenomenon of waves where waves from two different coherent sources superimpose at a given point and creates fringes.
Interference can be explained on the basis of wave theory of light only. Since two particle when collide will never disappear like we have in light waves which may give bright or dark fringes when superimposed. So, particle nature of light fails to explain interference