How to summerize address

How can I use interfaces loopback to summerize 2 or more network or subnet address?

We can use interface loopback to summerize 2 or more network or subnet address that been given to us to summerize.

Ok, for  you want to summerize these 3 subnetwork addresses:
172.30.1.0/24
172.30.2.0/24
172.30.3.0/24

First, assign each interfaces
R1(config)#int lo0
R1(config-if)# ip address 172.30.1.1 255.255.255.0
R1(config)#int lo1
R1(config-if)# ip address 172.30.2.1 255.255.255.0
R1(config-if)# int lo2
R1(config-if)# ip address 172.30.3.1 255.255.255.0

and then show ip route, like below: