The breadcrumbs are the links above the left sidebar, which form some sort of a trail to make it easier to navigate throught the site.
This is particularly handy when going through the grammar pages.
To edit the breadcrumbs, you have to click on the corresponding link in the translator's menu.
The translator's menu is only visible when you are logged in.
When you click on the link Edit the breadcrumbs, you will see the following.
You can see two editable sections.
If you click on the first 'edit' link, you will see something like this:
The underlined text (which I only underlined for the sake of clarity) is the only text you need to edit. If you already read how to edit links, editing the breadcrumbs should not be a big deal.
You do not need to edit the text under the second 'edit' link. This section contains code that makes the breadcrumbs display the title of the page you are currently viewing at the end of the trail.