Ephemerality means things that don't last for a long time.
Remember when you drew with chalks on the sidewalk? The pretty pictures you created didn't stay forever, right? They faded away after some time. The drawings were ephemeral. The bubbles you blew with your bubble wand also didn't last for a long time. They popped quickly. That means they were also ephemeral.
Some things in life are supposed to last forever, like buildings, trees, and mountains. But other things are not supposed to last for a long time. They are there to enjoy and appreciate for a brief period, and then they disappear.
Ephemeral things include sandcastles you build on the beach, flowers that bloom only for a short time, and clouds in the sky that keep changing their shapes. Even some art installations, like graffiti or sand sculptures on the beach, are created to last only for a while before they are washed away or removed.
So, ephemerality is all about appreciating and enjoying temporary things that don't last for a long time.