陕旅版六年级下册英语第三单元的主题是“My Family”，主要学习与家庭成员相关的词汇和句型。以下是本单元的知识总结：

1. 词汇：

- 家庭成员：father, mother, brother, sister, grandfather, grandmother, uncle, aunt, cousin

- 职业：teacher, doctor, nurse, driver, engineer, farmer, worker, singer, dancer, actor, actress

2. 句型：

- 介绍家庭成员及职业：My father is a teacher. My mother is a doctor. My brother is a student. My sister is a nurse.

- 询问家庭成员及职业：What's your father's job? What's your mother's job? What are your brothers' jobs? What are your sisters' jobs?

- 描述家庭成员的外貌特征：My father is tall and strong. My mother is kind and beautiful. My brother is handsome and smart. My sister is cute and lovely.

3. 语法：

- 一般现在时：表示现在的状态或经常发生的动作，如：He is a teacher. She works in a hospital.

- 动词第三人称单数形式：在一般现在时中，当主语为第三人称单数时，动词要变为第三人称单数形式，如：He works. She teaches. It dances.

4. 文化知识：

- 了解不同家庭成员的称呼和关系，如：father (爸爸), mother (妈妈), brother (哥哥/弟弟), sister (姐姐/妹妹), grandfather (爷爷), grandmother (奶奶), uncle (叔叔/舅舅), aunt (阿姨/姑姑), cousin (表兄弟/表姐妹)等。

- 了解不同职业的特点和工作内容，如：teacher (教师), doctor (医生), nurse (护士), driver (司机), engineer (工程师), farmer (农民), worker (工人), singer (歌手), dancer (舞蹈家), actor (男演员), actress (女演员)等。

通过学习本单元的内容，可以帮助学生更好地了解家庭成员之间的关系，学会用英语描述家庭成员及其职业，培养学生的口语表达能力和交际能力。