How Astronauts Use Laptops on the International Space Station
When the ISS was being designed, its architects wisely concluded that installing physical interfaces into the structure of the ISS was not a good idea. It's very hard to upgrade and/or repair interfaces that are part of the vehicle, whereas if laptop computers are used, upgrading or repair is as simple as launching a CD-ROM, uploading a file, or replacing the laptop. So with the exception of emergency hardware (e.g. ventilation valves), comm panels, and a limited set of other hardware, almost all vehicle commanding is done via a laptop interface.
There are, last time I checked, about 80 laptops deployed throughout the ISS. Most of them are Lenovo T61P laptops, but there are still a few old Lenovo A31p Thinkpads floating around.
The formatting of the laptop depends on its assigned purpose. On the US segment, commanding to the vehicle is done using laptops called PCS (Portable Computer System). They run on a linux operating system and are connected to the vehicle 1553 system as remote terminals. There are usually seven PCS laptops deployed throughout the vehicle.
On the Russian Segment there are about seven equivalent laptops called, simply, "Russian Laptops". They, too, are linux based, and are used to command the Russian elements.
Both the PCS and Russian Laptop use their own graphical interfaces that depict the ISS and the crew click on the module they wish to interact with and the system, and then the specific piece of hardware.
There are eight laptops in the Japanese modules that are provided by JAXA and use their own interface and there are two in the European modules that use their interface. There are about a dozen laptops used for payloads operations.
The remaining laptops are part of the Ops Lan network. They are called SSC (Station Support Computers). They are Windows based and are not connected to the ISS 1553 system. They are used for everything from viewing procedures, performing supply inventory, recording notes, sending e-mail, video conferencing, on down to Twitter.
In the above picture, three laptop screens are visible. The closest to Shannon's head is being used to view the procedure for the robotics activity she is performing. The one above and to the right of that is current displaying the SSC desktop. She is likely using that one to view the mission timeline. In the bottom right corner of the picture is a PCS. It looks like she has navigated to the US Airlock page, and while nothing is currently in alarm, it looks like she has a caution message to acknowledge. It looks like there was a brief loss of comm with a power supply.
We can also see a few of the built-in ISS interfaces, in this picture. Over the hatch is the Caution & Warning Panel and directly to the right of Shannon's face is the ATU (Audio Terminal Unit) (radio/intercom). And, of course, the big panel in front of her is to control the robotic arm and external cameras.
Here's an example of a system page (my system, Motion Control):
This screen gives a health and status overview of the Motion Control Group (combined US MCS and RS ????). Starting from this screen, the crew can access and control any piece of guidance, navigation, control, and propulsion hardware and software on the vehicle (well, Russian hardware commanding would need to be done from their laptop).
Top image via NASA
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This answer has been lightly edited for grammar and clarity.