calm down
The German phrase 'beruhige dich' is used to tell someone to calm down or relax. It is a command, so it is used in the imperative form. It can be used in a variety of situations, from calming down an upset friend to telling yourself to relax in a stressful situation.
Calm down, it's just a spider.
This phrase can be used when someone is overreacting about something that you view as insignificant or not worth worrying about, in this case, a spider.
Please, calm down and listen to me.
This phrase is commonly used when you need someone to be less agitated and to focus their attention on what you are about to say.
He said to her, 'Calm down, everything will be okay.'
This phrase could be used in a scenario when someone is trying to comfort another person who is distressed or upset, reassuring them that things will improve.