I had to poke around a little to figure it out too. Here's the skinny if you haven't already figured it out.
The plugin works by adding a new option on the right side of the Add/Edit Page forms to create a new Sidebar or select a sidebar that has been created already. Once created, the new sidebar is edited in the Appearance/Widgets area of WordPress.
1) After installing the plugin, you go to Settings / Reading on your admin menu. Then select a default sidebar (any will do - usually the main one) at the bottom of that form and save the settings.
2) Now make a new Page (it does not work with Posts), give it a Title and Publish it or Save as Draft.
3) You will see an option on the right side of the Page form called 'Sidebar' - with a drop box to select an existing sidebar - or a Link to create a New Sidebar. Click the 'Enter New' link and type a Name for your sidebar and click the Update Button.
4) You will then see a new link to "Update Widgets Now". If you have already saved your page, you can click the new link and you will go to the Widgets area of the WordPress Admin where you will see a new Sidebar with the name you gave it previously.
5) In the Appearance/Widgets area, add some widgets to your new sidebar. The new Page you created will reflect the new sidebar - and the new sidebar will be available to use on other Pages you create.
6) Sidebars will be DELETED if they are a) No longer referenced by ANY Pages. ie- you selected another sidebar in the drop box and saved the Pages. or b) If you Permanently Delete all Pages that use the sidebar. If you only "Trash" all the Pages that have the sidebar you made, it will still show in the Widgets area. You still need to delete the Pages 'permanently' for the sidebar to disappear from the Widgets area.
Hope this helps