if your using doombuilder, follow these instructions.
Make 2 sectors,
tag the sectors to themselves, (not eachother, for example, tag 1 to 1, tag 2 to 2)
make a control sector,
Select one line in the control sector
make action 97, (linedef executor, trigger linedef)
tag that line to the sector you want to teleport from, (that line will turn green)
make the sector you teleport from action 975, (trigger linedef executor, floor touch. when you scroll over the green line, the sector it's tagged to will light up yellow.)
select another line in the SAME control sector,
make it action 104 (teleport player to tagged sector)
tag that line to the sector you want to teleport to,
put a teleport destination thing in the sector your teleporting to.
your player will teleport to the spot where the teleport destination is.
your player will be facing the direction the teleport destination is pointing.
Dont forget to add floor, ceiling, and wall textures!
PS: to tag to sectors, lets say uhh, sector 1, to tag somthing to that sector, type 1 in the tag box OF THE sector/line you want to tag to that sector. K?