This tutorial assumes you have Thesis 2.1+ installed and active.

You can add breadcrumbs to Thesis 2 with this PHP box:

Install the box and add it the various templates templates via the Thesis skin editor into the Content Column box area (or similar area to get it where you want).

Then we would use Yoast SEO plugin to add our breadcrumb functionality.

Once WordPress SEO is installed go to SEO -> Features -> Advanced settings pages and click Enabled and save changes.

Then go to SEO -> Advanced -> Breadcrumbs, click enabled and Save to turn on the Yoast breadcrumbs.

Scroll down on that page and visit the "How to insert breadcrumbs in your theme" link to grab the PHP code they list and copy it.

Visit Thesis -> Skin Content and find the new PHP box options link (you won't find anyting until you add the box via the Thesis 2 skin editor as explained above) and click it and paste the breadcrumb code in.

There's other plugins you can use the same steps with as well to see how they work, i.e: