When you’re on your site, there will be links at the top right – above your username – for different admin areas. The link you want is the Widgets mode link. (If you don’t see this, make sure you’re 1) logged into an account with admin permissions and 2) have clicked the ‘Show Customization’ link next to your username.)
Clicking that link puts you into Widget editing mode. Buttons will appear to add widgets to each column on the site, and there will be an option at the bottom of each individual widget to remove it or customize it (some also have an edit button, but that’s a different article).
Once you have added the widget with one of the green button that appears on the site itself, you will want to click the ‘Config’ button below that specific widget. That will bring you to the customization menu for that widget, which lets you change the name and any options for the widget in question.
At the top of that menu, there are two options. By default it’s on the ‘Widget Configuration’ portion, but there is also a link for ‘Visibility’, which will let you set which sections on your site that widget will appear on and who will be able to see the widget.
In addition to the standard areas available on any site, like the forums or the image gallery, any custom sections that you have created on the ‘Site Structure’ tab of the admin menu will also be selectable.
Once you have chosen your visibility options, all you have to do is click ‘Submit’ and the changes will go live on your site!