How we cite our quotes: (Chapter.Page)
Quote #1
"Supposing I told you I'd been in a place where animals can talk and where there are—er—enchantments and dragons—and—well, all the sorts of things you have in fairy-tales." (1.7)
For The Silver Chair, the "other" stands for "otherworld." Narnia is a place straight from a storybook, and Scrubb knows that it will be hard to describe to Jill, and for her to believe him.
Quote #2
They had expected to see the gray, heathery slope of the moor going up and up to join the dull autumn sky. Instead, a blaze of sunshine met them […] It made the drops of water on the grass glitter like beads and showed up the dirtiness of Jill's tear-stained face. And the sunlight was coming from what certainly did look like a different world—what they could see of it. They saw a smooth turf, smoother and brighter than Jill had ever seen before, and blue sky, and, darting to and fro, things so bright that they might have been jewels or huge butterflies. (1.12)
It's clear that the children are in a new and different world, but we also understand here that they are the foreigners. The grubbiness and dirtiness of their world becomes noticeable in the clean, calm, and beautiful setting of Aslan's country.
Quote #3
And before [Jill] quite knew what was happening, [Scrubb] had grabbed her hand and pulled her through the door, out of the school grounds, out of England, out of our whole world into That Place. (1.13)
If you're going to journey into the otherworld, you've got to find the portal to get in, and in this case, it's literally a door. Lewis really wants us to understand that Jill and Eustace have left England and are heading into something truly different and foreign.