Its travelling this speed with respect to the Earth's Surface, and they get it to this speed by using rockets, that's why you need BIG rockets to launch things into orbit.
Getting something into orbit is simply a matter of speeding it up a lot. If you increase your speed you'll move to a higher orbit, decrease and you'll move to a lower orbit (Once you're up there of course...)
Its nothing to do with the Earth's magnetic field.
2ndly:
The astronauts are travelling at 17,227 mph AS well as the ISS (with respect to the ground) So they're travelling at a speed of 0 with respect to the ISS.
Think of it this way, When you're travelling at 70mph down the motorway and you have a cup of coffee in your hand, you're able to hold it and drink it without spilling it because it's also travelling at 70 mph with respect to the road.
But its not moving with respect to YOU inside the car.
Same deal with the ISS. (Just imagine the astronauts as very smart cups of coffee with tools)
Finally:
There's actually a small (tiny) bit of resistance up where the ISS is orbiting, but the atmosphere there is essentially 0. So yeah to a good enough approximation there is no air resistance on ships in orbit around the Earth.
This tiny bit of Resistance does eventually cause ships and probes to loose speed however. Generally over periods of about 50 years or so.
And this is called 'Orbital decay', most old satellites are just allowed to decay and they crash into Earth's atmosphere when they become non-functional.
Tiny tweaks here and there allow the ISS to maintain a stable orbit.
Hope this helps
