With a telescope
Please see related question for a complete listing of Jupiter's 40+ moons.
he was the first to see Jupiter
Jupiter has 63 confirmed moons. See link for further information about them.
You would not be able to see the moons from the surface; Jupiter's atmosphere is too thick.
You can see Jupiter's moons any night whenever you can see Jupiter, with the possible exception of times when the Moon is close to it. Just now (2014) Jupiter is mostly visible in midwinter.
His telescope did not contain the magnification necessary to observe Jupiter's lesser moons.
He saw 4 moons
Jupiter's many moons
Jupiter's moons do not have moons. No moon in the Solar System has a moon orbiting it.
Jupiter has 79 moons and there are 4 major moons; The Galilean moons named after Galileo.
Yes
there is about 70 moons of jupiter