[TYPO3] How to put in a extension in the template???

[Jes]

Hello

I really would like to put in an extension as an integrated part of a 
template - it is the login-in box. I know this can be done by adding som 
  code - something like ###text### - like a placeholder. I hope some 
kind person can direct me to some information about how I can do this.

I know it can be done - I have seen it somewhere - I just can't find 
information on how to do it.

Thank you and best regards

Jes Petersen