Alot depends on what you have, Are your inner rockers good? Are you replacing both inner and outer rockers? Are you using the OEM style rockers or the Replacement (over the top) rockers? If your floors are fairly solid, you do not need to brace anything to replace the rockers.this is my first car and first real body work.
how do I brace,from where to where and with what
How do you deal with the B pillar
The B pillar is spot welded to the top of the outer rocker. If you are using the OEM style rockers you will have to drill out the spot rivits, If you are using snap on rockers, they are notched for the B pillar. I would take measurements to assure yourself that you get the B pillar back in the correct place if you are using OEM replacement rockers. once we find out what you are doing we can be a little more specific