How to construct custom dataset with csv files?

I have read this doc https://github.com/sjwhitworth/golearn/wiki/Parsing-CSV-files, Something confused me, when I use base.ParseCSVToInstances read csv files how can I tell the api which colume is feature or label. Because not all csv file ended colume with label. Please show more examples please, Thanks a million @AlekSi @defcube @linkerlin