what is the basic difference between jobconf and job?
In short: JobConf and everything else in the org.apache.hadoop.mapred package is part of the old API used to write hadoop jobs, Job and everything in the org.apache.hadoop.mapreduce package is part of the new and preferred API to write hadoop jobs. Both APIs generally provide equivalent core functionality.
If you're new to hadoop just start using the new API (i.e. Job and Configuration instead of JobConf). Make sure to not import anything from the mapred package. When you find examples on the internet using the old API you can use this presentation or this guide to translate it to the new API.