Users can subscribe to the campaign with the purpose of receiving notification for new ideas and comments.
Subscribing to Campaign allows the subscriber to receive notification for all the new ideas and comments for the only campaign subscribed in case under profile notification 'New ideas' has 'Disabled' selected.
Steps to subscribe/ unsubscribe campaign.
 1) Click on the desired campaign. You will see Subscribe to campaign link under About Campaign Tab just below the Campaign Question / Challenge Statement. Click on this link to enable idea/comment notification for a specific campaign.

Another way to subscribe to the campaign is by clicking on the Star icon beside the campaign name which is visible when you are scrolling down a campaign page. Blue star indicates the campaign is subscribed.

2) Subscribe campaign is like a toggle switch. Once the user subscribes to a campaign, they would see the Unsubscribe from the campaign option. Click on unsubscribe link or click on the Blue star (unsubscribed will make it White) to stop idea/comment notification for a particular campaign.

Help article on campaign settings:

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