Vacuum is considered to be a free space in which not any force tends to act on a body; means an object is completely isolated from its surroundings in free space.
Where it is present?
Well above the surface of the earth at some altitude there is not any kind of forces are present, and overall space is a vacuum. Suppose if you go above the specific height of earth through rockets and space aircraft, then no gravity will act upon you and you will be like hanging object.
Vacuum in need
Astronauts, who visit space or satellites, tied one end of the rope with themselves and the other end with machinery, in order to go back to their respective place or rocket when the machine pulls them towards it because we can’t walk in free space.
Apart from space, we can artificially create a vacuum by some scientific means. NASA has already these kinds of labs in which they train their astronaut before sending them to space. As it is not easy to keep you normal in zero gravity and takes lots of practice.
Scientists and researchers also make prototype vacuum for their experimental work. Like, we have studied the speed of light and velocity of sound in permittivity of free space and then in other relative mediums.
An experiment in Vacuum gives accurate readings, a strong understanding of physical phenomena. Different instruments are used based on technical needs while performing different practical demonstrations. We come to know about tiny particles electrons, protons, and neutrons with the help of free space experiments done by many renowned scientists.