How to use checkpoint in script, vague information is available

I have created an internal data with name “internaldata” and added into checkpoint named “CheckPoint”.
I added below step in my script:
WebUI.verifyCheckpoint(findCheckpoint(‘abc_checkpoint/Checkpoint’), false)
Now with this test step, how do I identify on which field this checkpoint is working? what this test step will do?
Can anybody provide more information on this?
Test steps:
1. open browser and application url
2. sendkeys to the username textbox
3. Need to apply checkpoint on username textbox to verify username sent is correct.

How to perform third step?

as far as i understand this command compares whole snapshot to actual status e.g.
you defined checkpoint and you hit “Take snapshot” button in definition window this is now referential snapshot - all data as you defined (excel, db select, whatever)
now in test-case you call verifyCheckpoint -this will take another snapshot and compares it with referential one

Andrej Podhajský said:

as far as i understand this command compares whole snapshot to actual status e.g.
you defined checkpoint and you hit “Take snapshot” button in definition window this is now referential snapshot - all data as you defined (excel, db select, whatever)
now in test-case you call verifyCheckpoint -this will take another snapshot and compares it with referential one

Also you have option in definition of checkpoint to define which data will be taken in account in comparsion.