Hello,

I installed the Wordpress SEO Plugin by Yoast.

is the theme already supporting bredcrumb functions?
If not: How to use that?

The default header already has breadcrumbs.

You can also place it wherever you want. For more info, from dashboard > appearance > mz options, click the grey dropdown tab on the upper right that says limited php code. Then, in the left column, click bfa_breadcrumbs.