I dont get it could someone please explain: Energy from gravity...?

You can understand what apparently is happening on Europa if you just look at it like the Earth Moon system. The moon has an orbital period equal to it's rotation about its axis. THAT is why the same "face" stays facing us. Eventually, the Earth will stop just as the moon has already. Eventually, the Earth and Moon will have the same face, facing the other. The Moon, being only about 1/4 the size of the Earth, simply stopped first. What is happening is gravity causes the tidal bulge on the Earth. The Earth rotates faster then the moon orbits, so the bulge moves ahead of the Moon. The additional mass of the bulge off center ahead of the moon "tugs" on the moon, to drag it along, and at the same time, slowing the Earth's rotation just a little bit. This increases the orbital velocity of the moon, and it moves further away from the Earth. At the same time, the rotation of the earth slowed by a few microseconds.. At present, the moon is receding at the rate of about 1 inch per year as energy is lost by the earth, to the moon. And as a result, the Earth slows down by a few microseconds. Like water seeking its own level, energy that leaves the earth is received by the moon. On Europa, the same effect is happening. Remember one important thing, the earth appears solid, but it really is just a bunch of rocks packed together like a snowball, and exactly like a snowball, can be reshaped by outside forces. It is obvious about the tidal bulge of the oceans, but the same is happening to the crust as well, just on a much smaller scale than the oceans. The earth has a liquid core, so while gravity tends to hold it in a spherical shape, it CAN flex under the moon from gravity, and it DOES. It is thought that this flexing by the moon is one reason why the core is still liquid instead of solid as is the core of Mars. Flexing the crust makes heat from friction. Europa is a more extreme case, being so small compared to Jupiter, that it flexes a lot in comparison, which means even greater heating from friction. We have the sun adding a lot of heat to the earth, but Europa is so far away, the sun is only a minor contributor to the heat input. Our moon likely resulted for a Mars size body hitting the earth with a glancing blow, which is probably where our rotation came from. The moon probably formed from the debris thrown around by the collision, at a distance of about 10,000 miles. The rotation of the earth was at that time about 10 hours. Tidal forces would have been huge. Now, billions of years later, the moon is out at 250,000 miles, and the earth rotates every 23 hours, 59 minutes and change. If it was exactly 24 hours, we wouldn't need leap years. Anyway, THAT is the way I understand why it is possible there is liquid water on Europa.