To stand up in English, you can say "stand up." This expression comes from the verb "stand," which means to rise to an upright position on one's feet.

Here are some examples of how you can use this expression in a sentence:

"Can you stand up and give us a brief introduction of yourself?" (你能站起来给我们简单介绍一下你自己吗？)

"The teacher asked the students to stand up and stretch their legs before continuing the lesson." (老师要求学生站起来伸展一下腿，然后才继续上课。)

"The audience stood up and applauded as the performer took their final bow." (表演者拜幕时，观众站起来鼓掌。)