Tumblr themes: Set up a tag dropdown in the navigation
You simply click the 'Edit theme' icon on the top right of your logged in home page to open the edit side panel.
Look for the panels named:
Show tag dropdown - this turns the feature on and off
Tag dropdown items - add the tags you want featured making sure you add a '+' symbol between each like so 'bicycles+cars+go karts+trains'
Tag dropdown name - this is the word you want to appear in the navigation i.e 'Tags' or 'Categories' or 'Work'