This would obviously have a "Las Vegas" tag

Adding tags to Flickr images makes it easier for people to search for a specific picture.

[edit] Steps

Wait until your image has been uploaded. If it successfully has uploaded, you will see a "Finished!" and it will ask you if you want to add a description. Click the link.
Change the title of the image to what you like, add a description, and tags. Separate each tag with a comma. Note that you can add up to 75 tags per photo and if you have over 75 tags and wish to add more, you'll need to delete & replace some with previous tag names. Some suggestions on how to tag an image, using the one on the right as an example.
- Who or what is in the image? duckling (or duck), pigeon, crackers
- Where was the image taken? Hawaii, <insert city name>
- When was the image taken? May, 2008
- What did you take the picture with? digital camera
- Describe other factors. fluffy duck, Ritz Crackers, feeding birds

View the individual image.
Look on the right hand side between the photostream/set selections and the "Additional Information" (for licensing). Click on "Add Tag".

[edit]Tips

In the Help Discussion board, there is a thread posted on more suggestions to enhance and come up with tags for your pictures. You can view the discussion thread from here.