(Click on Images to view it Bigger)
Go to Options
Check whether Address Guard Option is there or not
If it is not there (actually this is an option given in Yahoo! Mail Plus) but it is Free for Yahoo! India) to change your content to Yahoo! India
Go to Options ==> Account Information
Check what is your preferred content
If it is Yahoo! US click on Edit (Above that)
And click on the Yahoo! U.S link on the next page
Change the content to Yahoo! India and save
Accept the Agreement
Now go to options
There will be an Address Guard link Click on that, and choose the "Get Started Now" Button
Choose a base name which should be different from your yahoo id
click continue, and choose a base name which is available
Choose the keyword, read the direction on that screen
Choose the folder and Indicator color and needed options from the next menu (you can create a new folder from the page also, choose new folder from the drop down list )
Create More or go to the mail from the next window
Now you can make the changes or add new keywords by options==>Address Guard
If you are getting too many spam to this mail address, just delete the disposable address with the specific keyword, and create a new one if you want.
Read the following (this is from yahoo)
Create a base name for your disposable address
Since you'll probably be creating multiple disposable addresses and then deleting them as they get spammed, it's best to begin with a base name (such as "shopping") that's different from your primary address. To get started, go to the "Spam" section in the "Mail Options" page and then select "AddressGuard." Next, click "Create a Disposable Address."
Add a specific keyword
After you've created a base name, click on the "Add" button under "Disposable Email Addresses" and type in an appropriate keyword (such as "shoes") for this particular address. Click "Continue."
Decide where to direct messages
Use the pull-down menu to determine where messages sent to this address will be delivered. You can create new folders if you wish. Click "Set Up AddressGuard" when you're done.