You can then click on the arrow to move the column to where you want it.
When you are finished moving them around you just click on the icon again to make it close back up. Before you close it back up notice the Notification sounds that you can click or unclick. If you are wanting to be notified when someone tweets you, if you have it checked it will sound off for you.
Once you have them where you want them it will be easier for you to keep track of the hashtags that interest you. The first four I typically have up are Home, @ Me, #Wordmongering, and #Editmongering. I often switch out the last two if I am participating in something else like #FastDraft and #RevisionHell or as I am going to be beginning #OctPoWriMo in October I will be bringing that to the first four. Sometimes I slide back and forth between pages so that I can see what is going on in other columns.
Tip for using TweetDeck for building your platform - Click on any of the names within a column then decide whether you would like to follow them. If it is someone you have something in common with, they will often follow back.