Iscsiadm is open-iscsi administration utility allowing discovery and login to iSCSI targets, as well as access and management of the open-iscsi database.

It has a lot options, not easy to start with, here are some the most popular options I use, also can be a quick reference.

Discover available targets from a portal, mostly used

iscsiadm -m discovery -t sendtargets -p ipaddress

Example:
# iscsiadm -m discovery -t sendtargets -p pps11
                                                           [  OK  ]
20.12.1.147:3260,1 iqn.2015-01.com.fibrevillage.pps11:pps11.target1

Target address configuration 

Add a target address for dynamic discovery

iscsiadm add discovery-address 10.0.0.1:3260

Add a iSNS server address for dynamic discovery

iscsiadm add iSNS-server 10.0.0.1:3205

Add a static address for discovery

iscsiadm add static-config eui.5000ABCD78945E2B,10.0.0.1

Target address discovery

For dynamic discovered address

iscsiadm modify discovery --sendtargets enable

For iSNS discovered address

iscsiadm modify discovery --iSNS enable

For static discovered address

iscsiadm modify discovery --static enable

Log into a specific target

iscsiadm -m node -T targetname -p ipaddress -l

This command is equivelent to
/etc/init.d/iscsi start
Which calls
/sbin/iscsiadm -m node --loginall=automatic

Of course there is a different if you have multiple targets

Log out of a specific target

iscsiadm -m node -T targetname -p ipaddress -u

Similar to login, it's equivelent to
/etc/init.d/iscsi stop

which calls
/sbin/iscsiadm -m node --logoutall=all

Display information about a target

iscsiadm -m node -T targetname -p ipaddress

Display statistics about a target

iscsiadm -m node -s -T targetname -p ipaddress

Remove the portal address to receive information or statistics about all targets.

Display list of all current sessions logged in

iscsiadm -m session
Example:
 iscsiadm -m session
tcp: [2] 20.12.1.147:3260,1 iqn.2015-01.com.fibrevillage.pps11:pps11.target1 (non-flash)

It's similar to
/etc/init.d/iscsi status

which calls
iscsiadm -m session -P 3

-P 3 stands for mover verbal printlevel

View iSCSI database regarding discovery

iscsiadm -m discovery -o show

View iSCSI database regarding targets to log into

iscsiadm -m node -o show

View iSCSI database regarding sessions logged into

iscsiadm -m session -o show

You may find out more in real iSCSI setup case in 

  iSCSI target setupand iSCSI client setup