All your in-context editing is performed in Block Areas. These areas hold the content and functionality blocks that make up your web pages.
Click "+" from the edit bar menu. This will pop out the blocks pane from the left:
Find the block you'd like to add from the list of all available types:
Then drag that block onto an available block area. It will glow green indicating it is ready to receive:
The block that you select will then present you with a form. This form allows you to personalize the block to your site and situation. When you have everything the way you want, click add and the block will appear on the page. Some blocks have additional preferences that can be changed in the dashboard.