At the moment every human being is stuck on Earth, besides the six astronauts on the space station and the eleven astronauts that NASA 'supposedly' sent to 'another world'. It might not seem like it, but humanity is 'a sitting duck' just waiting for a mass extinction event to be thrown in it's direction. If humanity is forever confined to planet Earth, then it's only a matter of time before humanity is non-existent. There are numerous internal and external extinction event's that could spell 'D-O-O-M' for man-kind. They include stray asteroids, pollution, nuclear war, generic war, Donald Trump and many more. If humanity expands and establishes new colonies around the solar system and hopefully beyond someday, the chances of humanity being erased from the universe is substantially lowered. An asteroid thrown at Earth would allow people to evacuate to another nearby planet or if they do not, the colonies will re-colonize earth. So let's talk about the way's humanity could expand to other planet's and the advantage's and disadvantage's that brings.
At the moment everyone is looking at Mars as the obvious colony choice but let's steer our focus towards the Moon. A colony on the moon isn't that difficult. The Moon contains resources such as Alumina and Iron oxide which could be harvested and used in the formation of construction materials such as steel. Oxygen could be extracted from Alumina or silica which would solve the breathing problem. Astronauts could go to the Lunar base for a year and then return to Earth just like astronauts on ISS do. If water does exist in solid form(ice) in the permanently shadowed poles of The Moon then that ice could be harvested and converted into water which then can be used for growing food using hydroponics or it could be split down into hydrogen and oxygen for fuel and for breathing.
The Moon seems like a good launch site for deep space mission's. If steel can be manufactured on the Moon, it would allow astronauts and machines to construct certain parts of rockets and spacecraft. The Moon's gravity is one sixth the gravity of Earth which means the Moon's escape velocity is lower than Earth's. Earth's escape velocity is eleven kilometers a second, the Moon's escape velocity is only 2 kilometers a second. Rocket's would require a lot less fuel when launching from the Moon and bring cost's of cargo back to Earth or to future Mars colonies down dramatically. Eventually massive "Solar Field's" could be constructed to produce a huge amount of power.
Once we can manufacture, use and re-use rocket's and space craft efficiently, then Mars and the Galilean Moon's are with in the reach of humanity. At the moment the biggest obstacle is fund's and co-operation between NASA, ESA, JAXA and various other government and commercial space agencies. If we want to go to the Moon then it's highly likely that we will have to go together, it would be harder and more time consuming if everyone goes as a separate entity.