Tags are like bookmarks. They let you jump around to different places in your file that you might want to reference, like a class definition for example.
Create a tag like so: ":tag tagname". This tags the current line number with the name you provide. Alternatively, you can use the shortcut CTRL + ]. The tag name will be taken from either the character under your cursor, or if you've highlighted a word or phrase, it will be used.
":tags" shows you your list of tags.
# TO tag FROM line in file/text
> 1 1 LongTextAnswer 8 q = LongTextAnswer()
Each time I show my :tags I get this error:
E433: No tags file.
This may also explain why my tags queue only contains the most recent tag I create. Further reading reveals that the tags file is created by the program ctags. I'll try installing exuberant-ctags and see what affect that has on my operation.
sudo apt-get install exuberant-ctags
Restarting vim and trying the :tags command again showed that my tags file could still not be found. I found a nice little page that describes the rest of the process that one must go through to get your tags file set up. Follow the link to learn more.
On a related note, you can read ctags in python: