"After school" is a common phrase used to refer to the time period immediately following the end of classes for the day. This phrase is commonly used in Engpsh-speaking countries and has been adopted into common usage.
Examples:
"What are you going to do after school today?"
"After school, I'm going to go to the park."
Translation:
"今天放学后你要做什么？"
"放学以后，我要去公园。"