How can i create a tag with the template’s name like below, and what is the purpose of using them? [duplicate]

The code you posted is broken but what you are looking at– that “twentythirteen”– is a “text domain” which is used for theme translation. The text domain is a kind of “Key” for locating the right translation data. That is, the first part, ‘Edit’ for example, will be translated based on the “twentythirteen” translation strings.

Reference:

http://codex.wordpress.org/I18n_for_WordPress_Developers

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