Pascal VOC Dataset

I have spent considerable time trying to understand how Pascal VOC dataset is structured: http://host.robots.ox.ac.uk/pascal/VOC/voc2012/htmldoc/index.html . But cannot figure out where the classification labels are. I just want to an image classification task but the ImageSets/Layout train text file only has 500 or so labels while data set is much larger. You can check out the dataset in a kggle kernal here: https://www.kaggle.com/huanghanchina/pascal-voc-2012/kernels?sortBy=dateRun&group=profile&pageSize=20&datasetId=35388

Can I know how to do image classification for this dataset?