[kh99]

Use {param} for the text between the open and close tags, and {option} for the part after the equal sign inside the first tag (if you set "Use Option" to Yes). Note that the same tag name with and without the option are treated as two different tags (in other words, you could have [nimg] and [nimg=foo] tags that do entirely different things, although if you actually did that it would probably be confusing).