ok i wanna make in my map like a gait like in highground where when you get the atvs, you go through the gate, how do you make it swing open when you hit the gate?

that would be a device_machine..or at least a halo3 equivalent of a device_machine...just make a door but has the gate model and make it so it opens side by side. i dont know how to do this, because ive never tried it before but thats how i presume it would be done

The one on halo 3 highground opens with a switche. The one on halo 2 turf opens when you walk or drive into it.

So, you want the gate to open with a switch? Or do you want people to be able to collide with it to open it, like run through it with hogs or mongooses?
If you want a switch, you just need a regular door\ switch device setup. Script the door to open when the switch is pressed. I don't know if it can sync.
If you want actual collision, I think the only thing that would work is a vehicle, because the player can collide and move them, unlike scenery and machines. So make a vehicle with no seats, and moving parts to collide with. That will sync, because it's a vehicle.

no he means the fence inside the base, the one which you can plow through with the mongoose

oh that one... =\ i dont know on how to do that.

you'd have to give it physics, so it rebounds off your car, but anchor part of it to the ground, so that it stays in place. Maybe a scenery with physics attached to a marker on the ground... idk :P

me nether, caus im trying to make a highground bsp