command 较正式用词，强调权威性、全局性和强制性。
order 普通用词，侧重指具体的命令。
direction 正式用词，指口头或书面的指示或命令。内容不一定详尽，语气较缓和，不太强调强制性。也可指指导性的说明。
instruction 书面用词，指不容违反、不容推翻的命令。也多指包含具体说明的指示。
参考例句
1. An instruction to go to a subroutine. 一种转移到子程序去的指令。
2. To follow the process of work instruction. 按照作业指导书的程序工作。
3. Reed College at that time offered perhaps the best calligraphy instruction in the country. 那个时候，里德大学提供了也许是全美国最好的书法指导。
英英解释
n.
1. a message describing how something is to be done
2. the activities of educating or instructing; activities that impart knowledge or skill
3. the profession of a teacher
4. (computer science) a line of code written as part of a computer program
