Can somebody please help me with coding a program for online graph plotting using 'python flask'.
The program has to take as input a .csv file and manipulate it and plot it accordingly.

Maybe somebody can help when sees your efforts (code or at least pseudo code)

I'm a newbie to python. I'm just into coding this and my codes ain't working. So, I've decided to start from the scratch. It'd be helpful if I get a good advice to where to start from.

The program has to take as input a .csv file and manipulate it and plot it accordingly.

The Python wiki contains a section on plotting tools. Other than that your question is impossible to answer as we have no idea if it is a 2D or 3D, bar or graph, etc. At the very least you should include code to read the file into a data container, and a sample of the data you want to plot.