How to people at genius bars switch sim cards?

What do you mean how do they switch them? Are you asking how they access the SIM card in the phone? Or are you asking something else? Switching the SIM just requires you to open the SIM tray, remove the old SIM, insert the new one, close the tray.

What kind of device are you referring to, and explain if I have not understood exactly what you are asking.

ssrossiter wrote:

I'm confused...

Me too.

Insert a paper clip or similar object into the pinhole on the SIM tray, located on the right side of the phone. Push in on it, and the tray should pop out.

There is no "machine"...

ssrossiter wrote:

iPhone 5 to 6, but I wonder if there is a machine cause thats wht I heard

If you had an older iPhone, such as an iPhone 4, that took a larger SIM and you wanted to keep the same SIM, there are things (they look like sort of like pliers) that will cut down the SIM to the smaller size. However, it's generally easier to just get a new one. The iPhone 5 and 6, however, take the same size SIM. Removing them does not require a machine. I can't think how any machine could make it easier than it already is. And paperclips are cheap.

Apple Stores have a new machine for applying screen protectors.

There is nothing to download from a SIM in an iPhone.

I think you may be talking about something like a Cellbrite. These are machines you can hook up two phones to that will transfer data from one phone to another. What data depends on the phone and how the machine is configured. Usually, though it would be contacts, pictures and messages. But none of that is stored on a SIM. And, if you have your phone properly backed up yourself, you don't need that.

ssrossiter wrote:

I want to know if the folders are kept on the phone when yo put the sim card in

Lol I have games hidden in folders of my phone and I dont want my parents to find out.

No, no personal information is stored on a SIM. All that's kept on the SIM is the information that allows the iPhone connect to your cellular account.

ssrossiter wrote:

I want to know if the folders are kept on the phone when yo put the sim card in

Lol I have games hidden in folders of my phone and I dont want my parents to find out.

Dont judge me...

The content of the phone, such as applications and folders are saved in your backup. If you restore a new phone from the backup of the old phone, that will be transferred to the new phone. Otherwise, as Meg has already told you, the iPhone writes and saves no data to the SIM.

the only purpose the sim card has is to tie the IMEI number of the phone to your subscription with the carrier

if you change carrier you get a new sim, user data is not stored on the sim

ssrossiter wrote:

So basically if I haven't backed up my phone, I will lose everything?

Maybe. If the info is sync'd to your computer it will be fine

But see this -> Transfer content from an iPhone, iPad, or iPod touch to a new device - Apple Support

tell me what I keep on the sim card

Nothing.