1)Use lindef 104, have trigger tagged to a sector with effect 975 or 974, and tag the lindef to a sector with a teleport object in it.
2)Use a lindef like 106, tag trigger to a sector with type 975, tag the action to the sector that you want the floor to go down on. Set the floor and ceiling of the control sector to be the end height of the floor. Jump on the 975 sector, and the wall will go down. Make sure to have something behind the wall.
3)Be more specific. What do you uwant the script to do? In all cases, have a lindef 58 fof in the area you want the script to run, and use lindef 113 to run the script. The script file run is the file SCRXXYYY, where XX is the map number, and YYY is the floor height of the control sector. So, if it's on map 15, and the floor height is 152, the file run is SCR15152.