Hello Gowthamraj
Whenever the 0.0.0.0 address is used in this context, it has a special meaning. This meaning can be seen in RFC 5735. Specifically, for this address it states the following:
0.0.0.0/8 - Addresses in this block refer to source hosts on "this"
network. Address 0.0.0.0/32 may be used as a source address for this
host on this network; other addresses within 0.0.0.0/8 may be used to
refer to specified hosts on this network.
Now in the case of the lesson, because the host keyword is being used, it is the 0.0.0.0/32 address that is specified. So in this case, this address is used as the source address for this host on this network.
So these particular entries allow multicast traffic destined to 239.1.1.1 and 239.2.2.2 that originate from the local device, namely R2.
I hope this has been helpful!
Laz