Wikipedia:Template index/User talk namespace/Substitution

All user warning templates (in the category Category:User warning templates), as well as their shortcuts (in the category Category:Redirects from warning template), should always be substituted when warning vandals or testers. If you fail to substitute a template, a bot like User:BetacommandBot will do it for you; however, it's always best to simply do it the first time.

Workings and implications of template substitution
If you type the text  into a page and save the page, the result will look like this:

Welcome and thank you for experimenting with Wikipedia. Your test worked, and it has been reverted or removed. Please take a look at the welcome page to learn more about contributing to this encyclopedia. If you would like to experiment further, please use the sandbox instead. Thank you.

And every single time you click "Edit this page", the text  will always be there, even though the actual text of uw-test1 (shown above) may change over time. However, if you type text  and click save, the result will appear the same, but checking on the page's source code, you'll see this:

By placing the text  in front of the template name, uw-test1 was substituted. So if uw-test1 changes, the display of the page on which uw-test1 was substituted will not change.

See Transclusion costs and benefits for a further explanation with diagrams.