Although the rocket engineering is a complex matter, the main principles on how rockets are built and launched are fairly simple.
Try an experiment: fill a balloon with air and then let the air out. What happens? The air goes one way, and the balloon goes in exact the opposite direction. It is the same with rockets. Exhaust gasses coming out of the rocket push it in the opposite direction at very high speed. It requires massive quantities of fuel to provide enough propulsion and speed to overcome the Earth’s gravity.
Another DIY example is this: get a skateboard and a bowling ball. Stand on the skateboard and throw the ball forward? What happens? The bowling ball will go forward, and the skateboard would move in the opposite direction. However the skateboard with you on the top will stop sooner than the ball and won’t move as far. This is because of you. Because of your weight to be exact. The more the weight, the less will the skateboard move. Check this video by BBC to see how they put this experiment to a test.
Rocket engineers face the same issues at launch. The engineers have developed two and three stage rockets to make entering space easier, quicker and a bit cheaper. Modern space rockets weight hundreds of tones at launch and most of that weight is fuel. The rockets are designed in sections, where the first stages contain most of the fuel. As the fuel in a stage is exhausted, the part becomes nothing else but a dead weight. More weight means more fuel is required to continue the travel. So rockets must get rid of the dead weight. These parts separate and return to earth in either oceans or unpopulated areas.
However, a huge speed is needed to overcome the gravity. It is calculated that the rocket has to reach 28,000km/h to enter the earth.
The clever scientists are working hard to overcome that obstacles. They have found a very clever solution – to use other planets gravity as a sling-shot in order to reach the planets that are further away in our galaxy.
To reach Jupiter for example, scientists use Venus’ orbit and its gravity to gain a speed boost. They made the spaceship whip around the planer to get that boost. This method shortens the time needed to reach distant destinations.