If they have a small box somewhere, hit that up first, if not like my hill, just comit to the rail.
Most of the rails I see for beginners have the shittiest lips from snowboarders, so you're going to need to jump a bit, either way, jump and turn 90, land on the rail without your feet super close together, or you'll either catch an edge and fall forwards, or lean back too much and fall off. Another thing I've noticed with kids learning on small rails with crappy take-offs, is they start with both feet to the sides of the rail, so when they get on if they do, they're automatically sliding off the other side right away, just start right in front of the rail, and take-off with one ski on one side, and one ski on the other, so if you fail to jump, or turn 90, you'll either nut yourself, or ride with a rail between your legs, it's scary, but it needs to be done at all times for beginners, and don't go too slow, or the rail will be super sticky, and you'll just fall off, go at a normal pace. So start off 15 feet from the rail, go straight towards it, rail between your legs, jump, turn 90, land with both feet shoulder width apart, and both feet on the rail, slide it, and worry about getting off it when the time comes, that's the easy part. Good luck man.