How did water arrive to Earth and formed oceans?

It happened around 3.8 billions of years ago (At this point, the solar system was already 1 billion years old.).

All planets closer to the sun are very solid and dense, composed of rock and metals. The other planets that are farther away, are composed of gases, ice... So they are less dense.

But Earth at that point, closer to the sun and dense (4 billions years ago) was very hot and no water could be found, it was full of fire lava and volcanoes and so on.

All this happened because of two things; outgassing which was happening in the planet Earth and huge comets attacks, crashing with the Earth.
(Outgassing: is the process where rocks release gases, in the planet -this thing also helped create the atmosphere. Volcanic activity? Is outgassing, for example.)

Comets have ice (Just so you know).

So the thing is that at that point, Earth was so hot, that water stayed in gaseous form until Earth's surface cooled down. The ground on earth was too hot, so water couldn't be water, it had to be in gaseous form. When Earth cooled down, after million years, then water that was in gaseous form, started condensing and became rain, and that's how little by little we started collecting water in oceans, which were nothing before, just small puddles.

So why is the water salty in the oceans? Because as water started creating and entering the ocean (from the atmosphere > from rain) it brought also gases that had been evaporated from volcanoes and geysers and so on. Water also at this time, was flowing on the Earth (Which has minerals on the ground), brought the minerals, that's why it's salty.

And yes, in the universe there is ice (water) and other planets have water too, just in different states. The whole universe has probably water.

All took at least 1 billion years to happen :]