To add a widget to a dashboard you scroll to the bottom and click the add widgets button.
Then you have to give the widget a Title, choose the type of widget and decide if you want to use one of the standard templates or create an empty widget that you configure yourself.
You can also choose a shared widget if you have any of these shared with you.
Then press save and the widget will be added to your dashboard. She settings for that widget will automatically open and you can customise the widget if you want. Otherwise just press save again and