Hello @pradeep_07 ,
Nature drop down campaign is used to identify the type of campaigns you are deploying, Whether is is a recurring campaigns, periodic campaign or a one time campaigns. Its upto you what type of values you want in that dropdown.
With this value you can identify the campaign in Analytics.
To add more values to this drop down. Navigate to: Administration > Platform > Enumerations
Then search for operationNature and there you can add mode values by clicking on the Add button (highlighted below)
Thanks,