How to identify?
I am also new member here though, I don't think this is good way to create a topic, because I believe 99.9% of people here understand what supply and demand is and what they mean.
Simply put supply means surplus, while demand mean scarcity of an asset, item or thing. Both demand and supply is an event that happen with time.
For example when Bitcoin value was $1 per unit, Bitcoin was surplus then, compare it to now when Bitcoin has limited supply which brought about increased in it price and value, now is between $41k-$44k.
Both demand and supply are factor that affect price of a commodity.