A Tag Is A Post Label!
Tags are labels that you attach to a Wordpress post that help quickly describe what the post is about to the casual observer.
>> Please note that Wordpress Tags are not Categories! A Tag is different! <<
… but it’s easy to get confused.
When you create tags you should decide which are the major items that you are posting about in your posts and then create a tag for each one, so that the tags for the post you are writing are able to describe your new post in a very brief summary.
You only need to add a few tags when tagging your posts, say 3-6 to give a good idea of what your post is about and adding anymore than this would look spammy.
So What is the Difference between Categories and Tags?
Wordpres Categories are things you create to categorize a Group of Posts and they can be setup ahead of time before you start posting and in reality there will probably only be a few of them covering the whole theme of your site or blog.
In comparison Wordpress Tags are keywords or keyword phrases attached to an Individual Post to help describe it. There is a very good chance that you may add a new tag to a post that you’ll never ever use again, thus making it unique. However you may find that you use some tags more than once because they are appropriate and relevant to more than one post.
Tags can Help with User Navigation
Through the use of the Tag Cloud Widget you can allow your site’s visitors to see all the most popular tags used on your site together.
This has two different advantages. Firstly in allows someone looking for a post on a specific topic to see that one exists on your blog.
Secondly it allows that use to click on the relevant tag in the cloud displayed by the widget and then to see all the posts for that tag displayed.
Of course, in many cases there will only be one post, but this method gives your visitor direct access to it, and if there are more posts these will be listed too.
Tags on Posts are Easy to Add and Manage
When you are adding a new or editing an existing post in your Wordpress user area you will find it is really easy to add a tag to a post.
ADD NEW TAG
On the right hand side of the page you will see the TAGS box and from here you can create a new tag, find and use an existing tag or delete a tag already attached to the post.
You can add one or more tags by entering them into the Add box. Remember to separate them by commas if there is more than one tag in the box.
A tag can be a single word or a few words just as in a keyword phrase.
Click the ADD button to add the tags you enter into the box to your post. The tags will then be displayed under “Tags used on this post:“.
DELETE A TAG
To delete an existing tag from your post just click on the little X next to the tag and it will be removed.

ADD EXISTING TAG
To pick a tag to add to your posts, which has been used before, just click on the “Choose from the most popular tags” link to see a tag cloud of the popular tags currently in use on all your blog posts.
Just click on the one you want to add it and it will be automatically added to the tags used on the post list.
Managing Your Tags
Managing all the Tags that you have already used in your Wordpress posts is also very easy.
You can access your tags via the TAGS Menu Option in the POSTS section of the Wordpess admin dashboard menu.
When you click on the Tags link you will see a whole page dedicated to the management of tags displayed.
Everything you need to do with tags, except for adding them to posts which you can do in Edit posts, can be done on this page:

This page allows you see all the current most popular tags in use, add new tags, search for tags, edit tags and their slugs and visit the posts where an individual tag is used.
It is not often that you will need to use this page but it’s good to know it’s there if you need it.
So that’s it for tags – if you have any questions please leave a comment.




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Hmm – partially answers my question.
Is it desirable to use ‘key words’ just from within the post, of should you add additional key words – - or both?
For example, in a post covering aircraft, I would put aeroplanes and planes in the Post Tags list.
Is it preferrable to include the word aircraft from the text of the post in the Post Tags list?
It’s always best to use keywords that you already have in your post and these keywords should be “on theme” (ie closely related) with the main keyword you are targeting with your post.
(note: your main keyword should also be in the title of your post as well as in your post 3 or 4 times depending on post length – once at the beginning, once at the end and the rest in the middle somewhere).