[Flow] Flow: mysterious migration commands

[Jan Greth]

Hello Community!

I have some problems understanding the whole Floe migrationcommand 
(doctrine:migrate, doctrine:migrationstatus, doctrine:migrationexecute, 
doctrine:migrationgenerate, doctrine:migrationversion, ...)thing and 
hope you can help me clear things out. So here are my questions:

First, can you explain, what's the difference between doctrine:migrate 
and doctrine:update ?

And to get in depth with the migration stuff: Can someone explain in 
simple words, what migrations in Flow are? When do i have to use it? And 
what ist the preferred Workflow?

I often simply read "instead of using doctrine:update use 
doctrine:migrate"... why?

I hope someone can help me,
greetings,
Jan