Usage is:

{{subst:CSDNotice|articlename|reason}}

For example:

{{subst:CSDNotice|foo|it is a page made only to attack}}

produces:

Hi, {{subst:BASEPAGENAME}}. The article you wrote, foo, has been tagged for Speedy Deletion, because it is a page made only to attack. If you wish to contest this, . Clicking that button will take you to the talk page where you will find a pre-formatted place for you to explain why you believe the page should not be deleted. You can also visit the article's talk page directly to give your reasons, but be aware that once tagged for speedy deletion, if the article meets the criterion, it may be deleted without delay. Thanks! ~~~~