before i had my accident i was practicing board slides some.one part i dont understand how do you get off the rail and do the 90 degree turn do u jump off the rail and then turn 90 degrees?i can do 50-50s with no problem at all i  just need help with board slides please.

Dude just make it up yourself.  Whatever feels more comfortable.  It's not like you have to do it one specific way.

i tried to jump the jump off the end of the rail, just hop off as you reach the end and spin out

If you can ride switch fairly well, then try doing a board slide to fakie. That was you continue your spin. start by sliding just the last foot or two untill you get comfortable with geting on and off the rail. Basically its just practice.