Homing in Marlin

Hello, I am hoping for a response with someone familiar with the Marlin code... (by this, I mean the Delta modifed Marlin code from Johann - its for a mini Kossel)

My questions have to do with homing.

When using the full Graphics LCD interface, what exactly happens when you press "autohome" as a menu selection under the "prepare" menu item? Does this just execute a G28, or something else?

In either case, what exactly is supposed to happen when homing is executed? I gather that each axis is increased (direction as defined in configuration.h) until it the max homing switches are triggered for each axis. Then what? On mine, the carriages stop just as soon as contact is made and the stops with the switches still depressed. I have read of a behavior where it then is supposed to back off and try again slowly for accuracy. Just for documentations sake, could someone who knows where this code is in Marlin take a look and describe just what is supposed to happen? What variables are then set by this and how are they used later?

Please include the file and location in the code that does this, if possible.

Thanks in advance,