From the "Layout" wizard, find any link to "Add a Gadget".
Choose any one of dozens of interesting and useful accessories, from the Blogger gadgets library.
You might want to note several details, for best results.
The "Add a Gadget" concept has an interesting history.
Occasionally, we see concerned bloggers asking about their inability to add page elements to their blog.
Besides several key settings in the template, there's a naming problem, which surfaces occasionally.
When I go to the dashboard Layout wizard, I'm given the option to "add a gadget" but not to "add a page element." The Add a Page Element button has never been displayed since I started the blog, so it's not something I broke myself.
Long ago, "gadgets" were called "page elements" - and the "Layout" display was named similarly.
Long ago, we used the "Page Elements" wizard.
What everybody may not realise is that what Blogger used to call "widgets" are now called "gadgets", and adding a "widget" (weird term) / "page element" (boring term) is now called adding a "gadget" (descriptive term).
What we used to call the "Page Elements" wizard may be found as the "Layout" link in the dashboard. If you publish the blog using a dynamic template, layout customisations may not be supported - and you may not have "Settings - Layout".
Of course, there could still be cases where the "Add a Gadget" link doesn't appear, doesn't appear where you need it, or doesn't work for you. You still need to be aware of template restrictions, whether intentional or non-intentional.