For a novice, I wanted to know what would be the best method to measure volume of a mass on MRI images

There are a number of different tools you can use depending on your needs. A tool like FreeSurfer, for instance, can automatically segment a set of anatomical structures, for instance, but simpler tools exist for simple ROI drawing and measurement.

You may want to poke around the tools under "Segmentation" on NITRC:

http://www.nitrc.org/softwaremap/trove_l...

Christian