楼主是要讲解这个句子吗?
A program is a specific set of instructions written by one or more people,which direct the action of a computer system.
一个程序就是一组指令的集合,由一个或多人编写,用于指导计算机系统的动作.
A program is a specific set of instructions written by one or more people,
这个前半句是定语从句,完整的表达可以是A program is a specific set of instructions which is written by one or more people,在这里which is 可以去掉,不影响句子的意思.
which direct the action of a computer system.
后半句是非限制性定语从句,一般是起补充说明的作用,去掉也不影响句子的整体性.像这句,如果去掉的话,前半句的意思就是一个程序就是一组指令的集合,由一个或多人编写.