From you administration page select the "Design" tab, and then click on "Layout". From there, you can chose the page you want to edit. After that, it's as simple as and clicking and dragging the features you want displayed in your Sidebar or Body! Once an item is in your sidebar or body box, you can customize it by clicking the little down arrow.
You can also add your own, fully customized sidebars. Scroll to the bottom of the page, and you will see "Number of Text Blocks in the Sidebar:" followed by a box in which you can type the number of the amount of boxes you want. You can do the same thing after "Number of Text Blocks in the Body". Enter the number of custom items you would like and click Save. They will now appear with the rest of your preset sidebar items, called "Text Block 1", "Text Box 2", etc. Drag them to your sidebar or body just as you would with the preset items. When you click the little down arrow you will see a text box in which you can type whatever you want, including HTML code. These boxes are great for announcements, embedable audio players, Faceboook and Twitter buttons, etc.