how drupal7 template engine work?
i am beginner in drupal and start learning drupal theming. i just need to know what is actual function of template engine inside the drupal system.and how it work to display the web page i search many site all tell generic answers like- it separate developer work from designer work.i just need more elaborate answer to grab concept behind template engine and template files.Means when we load drupal web page in browser what template engine do,and what happen if system have no engine. please tell all steps template engine do to render drupal web page 

thanx in advance 
how drupal7 template engine work?
===

i am beginner in drupal and start learning drupal theming. i just need to know what is actual function of template engine inside the drupal system.and how it work to display the web page i search many site all tell generic answers like- it separate developer work from designer work.i just need more elaborate answer to grab concept behind template engine and template files.Means when we load drupal web page in browser what template engine do,and what happen if system have no engine. please tell all steps template engine do to render drupal web page 

thanx in advance 