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Is the reason that I cannot see that functionality that I have too low reputation?
You need 1500 reputation now to create new tags.
There are 60,000 tags already available. Odds are what you need is included among their number.
Keep in mind that many seemingly obvious tags may be named different than you expect, to avoid ambiguity. For example,
Also remember that the point of tags on Stack Exchange is not to summarize your question, but rather to sort it into a set of well-defined categories. Tags are how your question connects to an audience of users qualified to answer it. These users will have certain tags marked as 'interesting' or subscribe to the rss feeds for their tags. If you create a new tag, that tag is guaranteed to not help attract any of those users.
A good rule of thumb is to check the auto-suggest prompts when tagging your question. Any tag with a number less than 10 (100 on Stack Oveflow itself) after it's name is more than likely wrong. If you feel you have a fairly common topic (take 'mssql' for example) and you see a very small number for that tag, try an alternate name (like 'sql-server').
You "create" a tag simply by using it on a post. If it doesn't let you, you don't have enough rep (you need 250 on SO; 100 on SF and MSO - if the FAQs are up to date...).