REREAD ALL PREVIOUS CHAPTERS! I'm serious; I made MAJOR changes to a bunch. (Specifically the ones including Cede.) Now, due to request, I'm going to give you the explanations for the whole switching process.
K, so two people (i.e. Kurt/Chloe or Mercedes/Cede) stand in the same spot (ie Sink in Girls bathroom or Window in Math room ect.) at the same time. The first time, they don't go though the 'Switching Portal' or whatever you want to call it. They just switch. From there on, weather it's you second time or you're ten millionth; you go through the 'Portal'. This is kind hard to explain, but I'll do my best.
You stand in the same spots, then wherever you're facing, changes to the other world. Your double will be standing there. You simply walk forward to switch. It's kind of like Through the Looking Glass. Just a little different. Once you switch, the 'portal/mirror/whatever' closes. You can access the portal anytime by standing in the same spots. BUT! You can only switch once a day.
It's not always a perfect science, sometimes phones can call each other over the portal, other times they break. Maybe bodies will switch rather than minds, other times you may get stuck. This will make sense in the sequels.
There is going to be an 'explanation' in the second one, Connected. So reread Switched and be on the lookout for Connected.
Bye!