The old friends reminisce about their school days every now and then.

every 意思是"每个"，now 意思是"现在"，then 意思是"那时"，and 是连接词"和"。 every now and then 是一个固定短语，字面意思是"每个现在和那时"，引申为"时不时地""偶尔"的意思。