The printing option is in the top-right corner of a tab's page, it looks like a default "Share" button.
Upon pressing this button, you will have four options to choose from.
1. Print option connects you to AirPrint Printers, so you can send the chosen tab directly to one of them.
2. Open with option allows you to export the text of the chosen tab to another application, e.g. to edit it in Pages or save to Dropbox.
3. Email option sends the link to the text of the tab to your email, so you can open it on any other device and print out from there.
4. Copy to clipboard copies the link to the text of the tab, so you can paste it somewhere else, like a browser or a text note.
Please note, that only text tabs and chords can be printed out in Tabs HD app. To print pro tabs, please see this page: http://support.ultimate-guitar.com/knowledgebase/articles/537478-how-can-i-print-tabs