I can slide the columns up and down to see more and less recent tweets, but I can also adjust the order that my columns are in, which I've explained later in the post.
In order to use tweetdeck, go to tweetdeck.com and then hit the "sign in on the web" button:
From there, you can use your twitter id and password and then customize the screen to be the chats and hashtags that you want to follow. When there's a chat or hashtag that you want to follow, add that column and you see all of the activity about it right there in one place. You can tweet right from tweetdeck, adding an image if you care to. Sometimes, when I am participating in a chat, I put the notifications column next to the chat, so that I can pay attention to the comments back to me. You can move the columns around by using the grey column on the far left, adjusting to have various ones side by side in what ever way helps you to pay attention to the incoming information.
If you are already on twitter, I highly recommend tweetdeck--add a few columns with some favorite hashtags. Given the fact that you are reading this post, I recommend #tcrwp, #twtblog, #educoach, #engchat, and #elachat, but sky's the limit--there's no shortage of information out there.
So much to learn!