How does network routing work, and why do we need a netmask?

Question

iptables

When I ran the ifconfig command, I accidentally noticed that the eth0 and wlan0 interfaces have different subnet masks, Mask:255.255.224.0 and Mask:255.255.225.0

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         10.8.96.1       0.0.0.0         UG    0      0        0 eth0
10.8.96.0       *               255.255.224.0   U     1      0        0 eth0
10.42.0.0       *               255.255.255.0   U     9      0        0 wlan0

Next, I paid attention to the meanings of Gateway, but how is Getaway related to Genmask?

Answer 1

Routing Table
From Wikipedia, the free encyclopedia

Answer 2

but how is Getaway related to Genmask

Under the word "default" the network is hidden 0.0.0.0, in total we get the route0.0.0.0/0