Every theme has a default setting. By adding widgets you over-ride the default widget setting in your sidebar. You sort this out here -> Presentation -> Widgets
Simply locate the widgets you want in the Available Widgets box and drag and drop them into the Sidebar box.
Then take note that each widget that the blue and white lines icon on it will open if you click it and once it does you can configure it to suit yourself.
Lastly, click “Save Changes” and then view your blog – VOILA!
When you first start a blog, there is a default display of widgets in the sidebar as an example. Once you go to presentation > widgets and install a widget into the sidebar, the default set disappears. Simply drag the additional widgets you want to use from the lower box to the sidebar box and arrange them as you wish and then select “save changes” and you are on your way.