A Star Engine is a device made for the purpose of activating FTL travel for starships. It is a complex and rigid machine, potent in energy and power. It is one of the most important machines in human space, if not the most important.
Before its invention, it is assumed that humanity was limited to the Solar System and surrounding systems only. During this time, humanity used less advanced engines to travel across space which would take decades if not centuries to complete. When the Star Engine was invented not long after the discovery of the Fifth Dimensional Elements. Its creation was the most important technological advance in human history, allowing mankind to travel across their part of the galaxy and began the Age of Exploration
This is a very simple explanation of the Star Engine; other factors have not been accounted for.
The Star Engine is made up of almost nothing but FDEs, however the most important element is Kalenium. Kalenium is the most energic of the elements and has a strong connection to the Fifth Dimension. It is tied to the fifth dimension by a 'rope' of sorts from every direction. When subjected to extreme cold (-600 celsius), it defies the very laws of physics and time, jolting at speeds faster than light in a random direction.
However, the direction it heads to can be controlled, if placed within a tube made of marium. When electric surges run through the tube at one of two directions, the kalenium flies in that direction. Where the ship wishes to go determines on how the tube is turned. However, whether it works or not determines on the size of the ship and the kalenium sample. If it is a ship such as a Heavy Battleship, a much larger amount of kalenium is required, as well as a larger tube, whereas escorts usually only need several pounds of kalenium.
When activated, the ship looks as if it has instantly disappeared. However, this is because the ship has jumped into speeds incomprehensible to the human eye, yet it has still disappeared. But it is not in the material dimension anymore, instead it has entered the fifth dimension.
The fifth dimension is a dimension outside the boundaries of physical space, and yet still inside it. It is a realm of colors unknown to the human eye, and shapes and sizes no one has been able to comprehend. It is the reason why only the most trained are allowed to command and pilot a ship, as a regular person viewing the things in the fifth dimension would likely traumatize and confuse their minds.
Time is also skewed during travel as well. People inside ships travelling with the Star Engine travel at 1 lightyear per minute. While to them, traveling from Sol to, say, Alpha Centarus would take only four minutes, to people in Centarus, it would take four days. While things are quicker in the fifth dimension, it is not the same as in the material dimension.