php - How does Magento Install,Update scripts Actually work? -

i researched lot 5 hours.

i referred code given here add new attribute magento database customer.

for used install-1.0.0 script. needed other fields add database created update script upgrade-1.0.0-1.0.1 , added <version>1.0.1</version> own extension " stackexchange_customer/etc/stackexchange_customer.xml

but still fields not getting added in db.

there no clear guide regarding

1. how install script works , update script works??

2. which call goes file ??

3. when update, install module called ?

4. does called when enable/disable module ? or else ?

   magento complex, without proper documentation on net , stackoverflow , has become more complicated.

thanks.

here best article alanstorm: http://alanstorm.com/magento_setup_resources

also explained here well: my magento extension install script not run