Vượng phan hữugraphgivenillustrates
The line graph given illustrates (poor word choice) the amount (wrong word. Amount is for non-count things.) of Chinese inhabitants (That could be the Chinese people living in Vietnam or in the United States. Your expression is not good.) taking four 4 (redundant,) types of course. (wrong form)
You have not read my advice. Wrong use of vocabulary words! The reader expects that this graph has ONE curve - those Chinese people taking four kinds of classes.
You use the wrong words: figure and witness. Read my advice about these words.
Consider the following opening paragraph. It clearly describes the graph: the time period, the subject, the units of measure, and the four different curves on the graph.
The graph compares the numbers (in millions) of inhabitants in China who are enrolled in each of four types of courses (undergraduate, postgraduate, online training and literacy) between 2006 and 2012.
Thank you for that, I'll notice those mistakes