How in the heck do you open the gym in the school level I know you have to slide down the open sesame rail but whats the trick ???? Thanks In advance

You have to time it with the ringing bell. I don't know the exact timing, but you either have to be sliding or end your slide when the bell rings.

I think you have to rail it during the 2nd bell ring. I think this is around 1:40 left in the game.

Where is the open sesame rail? Is it the two right in front of the gym door?

In the big indoor skatepark, I forgot what it's name is, but it's the one with the huge wave ramp and the deep halfpipe. Anyway, how do you get the 2nd chain link fence to open?

Ok, to get the gym to open the rail to grind is one of the 3 grinds needed for your goals ( i forget the name). When you start the game, go to the right and down to the school yard. It is the one with steps on one side and ramp on the other. It is a pretty long grind. It heads towards the gym.
To get the fences to open, grind the one rail to left at the begining, it kind of loops around and connects the half-pipe. The other one, go to the big wave part, grind it to the left and jump at the end, then grind the rail you land on.
Sorry if my descriptions aren't the great, but it's been awhile since I played THPS2.