This link describes the way back from the Moon surface to the orbiting spacecraft. But how could that spacecraft get back to the Earth?
It is a long journey. How much rocket fuel would be needed, in terms of tons?
Where is a technical description of this?
It’s a long journey, but it’s all “downhill” — once the spacecraft leaves the moon’s gravitational sphere of influence, Earth’s gravity brings it home.
The process of leaving the moon is called “trans-Earth injection” or TEI; the rocket engine on the CSM fires for about two and a half minutes, adding about 1000 m/s to the spacecraft's speed in lunar orbit, burning about 10,000 lbs (4.5 metric tons) of propellant in the process.
This is an extended comment on jumpjack's answer, because it raises an interesting question and it's too long for a comment. The interesting question is:
how much energy does a spacecraft returning from the Moon need to lose on atmospheric entry, and how does this compare with the energy required to launch the spacecraft?
Well, we can answer this, and as is traditional I will take Apollo 11. Based on the Apollo 11 flight journal, the speed of the CM at the entry interface was $11045\,\mathrm{m/s}$. From NASA the Apollo 11 CM mass was $5557\,\mathrm{kg}$.
If we assume the CM was stationary after splashdown then the amount of energy lost is then $3.39\times 10^{11}\,\mathrm{J}$.
Well, the energy density of kerosene (from Wikipedia) is $43\times 10^6\,\mathrm{J/kg}$, so the energy lost by the CM corresponds to $7880\,\mathrm{kg}$ of RP-1.
So, then, the S1-C carried about $770\,\mathrm{m^3}$ of RP-1, and the density of RP-1 is about $850\,\mathrm{kg/m^3}$: in other words the S1-C carried about $654\times 10^3\,\mathrm{kg}$ of RP-1.
So the energy lost on the way back through the atmosphere is about $1.2\%$ of the energy available in the S1-C.
The spacecraft must accelerate enough to have its centrifugal force overriding the Moon's gravity, thus escaping lunar orbit. With proper calculations, the orbit is left when the spacecraft is closer to the Earth, so it eventually get caught by Earth gravity and pulled back.
But this is just the "easy" part.
Then the spacecraft must lose all the energy that the rocket had put in it when launching from Earth! If an engine was used, it would require almost the same amount of fuel used to launch the spacecraft. So, rather than slowing down by engine, the spacecraft gives its energy back to Earth system, by using air friction: the "potential energy" (mass * 9.81 m/s2 * altitude) and the kinetic energy (0.5 * mass * velocity2) are converted into heat, which is dispersed in the atmosphere.
Some spacecrafts use only air friction to slow down, other ones (modern ones) also use retrorockets in the final part of the landing procedure.
