Conservation means protection, safekeeping, maintaining a level or quantity, avoiding destruction (extinction) , safeguarding some thing.
For us on the Earth, what matters is the resources that enable life. These resources are oxygen, (pure air), pure water, environment, biodiversity (different species and organisms), minerals, fuels, energy etc. Most of these resources have their recycling duration and regeneration procedure, in a natural way.
Without the man's modern ways of living, use of chemicals and fuels, and also when the population on Earth was less, the environment and biodiversity were protected and conserved naturally.
With the exponential use of fuels, and other natural resources on Earth, we are continuously reducing the quantities available to the future generations in our world. We are also reducing the ozone layer in the stratosphere.
So the motto , slogan "Conservation is Survival" means that all people on Earth must put forward their efforts to use the methods that protect and manage the resources in a conservative way. The preservation allows future generations to live on Earth. Or, after some 100's or 100's of years, the life on Earth could become very difficult. Perhaps after a long time the life could become extinct as the living conditions for life do not exist anymore.