destined +

Text :
Forward Chain : Filters packets destined for networks protected
by the firewall.
Meaning :
Filters packets that are determined beforehand for networks
(it not "the networks") protected by the firewall.
I think it is the private networks.
Packets that come from the outside world into the private network.
A firewall is normally a firewall for outside world and not for the private network.
Table comes first and then comes Chain.
Table here means a set of data arranged in rows and columns.
Filter chains means to restrain using a series of related or connected
facts,events etc.

P.S I do not guarantee about the correctness of the above statements.