you是名词,“你”的意思~your是所有格,表示“你的”
are your 和 is your 按你说的就是单复数的区别,如：
Your books are heavy.====> Are your books heavy?
Your book is heavy.====> Is your book heavy?
book是单数,books是复数.
you是表示“你”的意思,一般没有is you这种说法,例如：
You are a student.====> Are you a student?