The first object that reached low Earth orbit was the Sputnik, which started the space race. By then, many satellites got to orbit around Earth.
These are the activities to do while in Earth orbit.
Reaching orbit[]
There are two articles on this subject: Low Earth orbit and Getting to Orbit.
Just like in the real world, most of the fuel of a rocket is spent to achieve low Earth orbit. From that point, it is relatively simple to go anything else. A failure in achieving a low Earth orbit will end up in a suborbital trajectory and burning up into the atmosphere.
What to do in orbit?[]
The first thing to do is to put an artificial satellite or a manned rocket into orbit. They can remain there for as much as you want.
As many players have shown, it is possible to build a space station. See the docking tutorial for more details. One can also experiment orbital maneuvers and aerobraking before advancing.
Players who don't achieve the paid version can still make two rockets get very close. One rocket can gently push another one, changing its orbit. This is useful when you try to reach Mercury, Jupiter’s moons or Venus, some of the most difficult celestial bodies to get there in the game. See Helping Vehicle for details.