This template is used similarly to {{tl}}, to show the name of a template with the open and close braces around it. But this macro makes the inner braces part of the link, whereas {{tl}} does not make the braces part of the link. This is to allow shorter template names to be easier to click on. The "Tn" name is short for Template name.

{{Tn|name}}

It will render this:

{{name}}

Compare with:

{{Tl|name}}

Which renders this:

{{name}}

There are several similar templates, these two lists most of them with some examples:

سانچو:Tl-nav