It is best to have an extra Yahoo ID (preferably that no one knows you by) usually referred to as a "bot" to login to YInformer with.  If you do not have an extra ID, you can go to mail.yahoo.com and sign up for a new one.

These are in reference to the numbers in red in the image above:

1. Put in your bot's username (exactly as it was created)
2. Put in your bot's password (exactly as it was created, case sensitive!)
3. You can have YInformer automatically log your bot in when you launch YInformer by checking that box.

After that, click the Login button on the right side and it will login your bot.

Extra:

Your username, password and the auto login settings will be stored once you exit YInformer.  That way you will not have to keep reentering that information over and over!

Troubleshooting Login Issues:

If you try to login and your bot icon stays gray, your bot is probably not logged in.  This could be a number of things including:  firewall/router restricting access all of a sudden, tcp/ip stack needs cleared (YInformer can do this for you on XP/Vista), pc needs restarted and/or Yahoo is patching login servers.  First thing to do is disable any and all security software as that is the #1 item that will block YInformer's traffic.  Next would be to run the System/PC Optimizer from YInformer (provided you have the appropriate operating system and YInformer will let you know). If that still does not work, it could be a patched server, in that case you will want to check out http://forums.programmingsource.net and see if there is a Bug Report posted or if others have posted about it.