Magento cache is used to speed up performance. The cached files is stored in
My doubt is how cached files are retrieved and shown in frontend.
Mage::app()->getCache() gives you a Zend_Cache instance, where you can do a lot of things:
save($value, $key, $tags = array(), $lifeTime=null) load($key) remove($key) clean($tags = array()
Magento does different things:
It stores the parsed XML configuration and layout to avoid parsing the XML files again
It stores the output of a block to avoid getting data and rendering HTML again (if configured so)
It parses the CSV files (and sort it through the different layers: Module translation, locale.csv) with the translation and stores it in cache to not parse it again
Magento can store collection data in cache, but afaik is this used nowhere...
It retrieves the EAV attributes and does something with it, don't ask me wh at.
The same as configuration: Parsing and merging xml files
It stores the whole page output in cache to avoid rendering the complete HTML again
I hope this answers your question.