In order to see your most recent 100 Twitter followers, just add a Twitter Follower column like this:

• Click the Add Column button 
• Click the Twitter button and select your Twitter account
• Click Core on the left hand side
• Click the Twitter Followers button

This will add a New Followers column to your TweetDeck.

To Follow the person back, click Follow

To Unfollow someone that you have already followed, click Unfollow

To Block the person, click Block. You can also Block by hovering over the profile picture and clicking either Block or Block & Report Spam