在上课时，要认真听讲并专心英语可以用 "pay attention to the lesson and focus on Engpsh" 来表达。
"Pay attention" 是一个常用的习惯用语，意思是注意，集中精力。例如：
Please pay attention to the instructions. 请注意指令。
Pay attention to what I'm saying. 注意我在说什么。
"Focus" 是一个动词，意思是专注，集中精力。例如：
She tried to focus on her work. 她试着专心于她的工作。
It's hard to focus with all this noise. 有这么多噪音很难专心。
所以 "pay attention to the lesson and focus on Engpsh" 的意思是在上课时注意听讲并专心英语。