祈使句用动词原形开头。
Sit down. 坐。
Come here. 过来。
Turn left. 向左拐。
Stop talking. 别讲话了。

如果是否定形式的祈使句，在动词前加上 do not 或 don't。
（Do not 更加正式，don't 更日常。）

Don't be late.
别迟到。
Don't go!
别走！
Don't push.
不要拥挤。不要推。
Do not walk on the grass.
请勿踩草地。

将上节课的句子变成否定形式的祈使句：
Sit down. —> 

Don't sit down. 别坐下来。
Come here. —>

Don't come here. 别过来
Turn left. —>
Don't turn left. 不要向左拐。
Stop talking. —>
Don't stop talking. 不要停止说话。/继续说。