The word "calm" is used to describe peacefulness or a lack of anger, especially in the face of a threat or danger. (Try not to pronounce the "l" in "calm.")
In these sentences, "calm" is an adjective:
The lake looks calm today. There are no waves.
Everyone remained calm during the emergency. There was no yelling or screaming.
The teacher addressed the unruly students in a calm manner.
The word "calm" is also used as a verb:
You should calm down.
The baby was calmed by his mother’s voice.
Music calms the savage beast.
The word "calmly" is an adverb.
The young man answered the questions calmly and without hesitation.
The priest spoke calmly during the service.
The sound of the ocean has a calming effect on people. (The word "calming" is also used as an adjective.)
You can use "calmness" as a noun:
Only time could bring a sense of calmness back to the community following the riots.
Our manager is known for his calmness when he’s under pressure.
A river has a calming effect on people who live nearby.
