I have been working my a** off trying to understand STP just fairly well. Its a hard topic, especially with Rapid STP. I have struggled with the synchronisation/proposal/agreement thing. It has helped seeing it on the equipment though.
An alternate port can be switched to immediately. If the root port goes down and the switch has a designated port, it performs the proposal/agreement bit, and another switch becomes a designated bridge for it. Nifty stuff.
MST (Multiple Spanning Tree) is also a good idea. Instead of running an instance of STP for each Vlan, you can group it together.
In order to do any of these tests, i had to copy an image of one of my 2950’s and onto another, since it was too old to support RSTP.
Now I really must learn to proceed without understanding the very last detail of some things. Some things are just not meant to be understood in detail, but only the differences. Im too picky regarding these things.