To exist is to live or to take some physical shape. Things that exist include people, animals, plants, buildings, ideas, etc. Things can exist in concrete or intangible forms. (intangible = It can’t be seen or touched). This is a good word to use when describing reality.
The word "exist" is a verb:
Plant and animal life can exist just about anywhere on the planet.
The idea that people of the world can live in peace still exists.
People of different religious backgrounds have to learn how to coexist. (co + exist = live with)
That building no longer exists. It was torn down.
Many animal and plant species no longer exist. They’re extinct.
Does God exist?
Do U.F.O.s really exist? (U.F.O. = unidentified flying object; alien spacecraft possible containing aliens)
Jeremy exists on ramen noodles. He doesn’t have enough money to buy healthy food.
Wooly mammoths no longer exist. They’re extinct.
The word "existence" is a noun:
That company was in existence for over 80 years.
The existence of many animal and plant species is threatened by global climate change.
Rhonda says she doesn’t believe in the existence of ghosts.
Do you believe in the existence of God?
The word "existential" is an adjective:
A large asteroid striking the Earth would pose an existential threat to all forms of life on the planet.