The verb 有 in Chinese can mean both possession and existence, like the English "to have" and "there is" or "there are":
她有漢語詞典。
She has a Chinese dictionary.
我們學院有多外國學生。
There are a lot of foreign students in our college.
N.B.:
To negate 有, one uses 沒 instead of 不:
我有哥哥﹐我沒有姐姐。
I have an elder brother, but no elder sister.
Informally in a negative sentence, 有 can sometimes be omitted:
我朋友沒(有)書﹐也沒(有)筆。
My friend does not have books, nor pens.
現在我們的宿舍沒(有)人。
There is no one in our dorm now.
The affirmative-negative question form is "... 有沒有 ... ?"
她有沒有妹妹﹖
呢﹐你們的宿舍有沒有人﹖
Sometimes, if the object of 有 is not long, one can use the form "... 有 + object + 沒有 ?" as well, although this form is not as common as the previous one.
她有妹妹沒有﹖
這宿舍有人沒有﹖