I can only tell you how blogspot does it and I am guessing that WordPress has a similar process.
Basically after signing in, I go into the layout section. There are several partly highlighted boxes around the screen that have the word GADGET in them. This just means that it is an allocated area that is free and can be used to add a PLUG-IN.
Plug-ins give you all sorts of extra things around your screen, such as a FOLLOWERS section or a VISITOR COUNTER or a LIST OF BLOGS THAT I FOLLOW or TOP 5 VISITED POSTS FROM THIS BLOG etc.
Just select the plug-in that you want.
Hopefully WordPress is similar.