Document Vector contains the frequency of each word of the vocabulary in a particular document.
In document, vector vocabulary is written in the top row. Now, for each word in the document, if it matches with the vocabulary, put a 1 under it. If the same word appears again, increment the previous value by 1. And if the word does not occur in that document, put a 0 under it.
Study more about Natural Language Processing at Natural Language Processing Class 10