Why you do not have guidance of seniors? Are you working alone in the purchase department? While choosing job you could have chosen such job where in seniors are available.
Anyway, to build your knowledge, you need to augment your knowledge base. For this, you may do Diploma in Materials Management (DMM) through Indian Institute of Materials Management (IIMM). This institute has chapter in each state capital. Go to Google to get details further.
There are training companies, who conduct 1-2 day training programmes on Purchase Management, Inventory Management, Negotiations Skills for Procurement professionals etc. You need to attend such programmes. You have not mentioned you are from what city, otherwise, I would have recommended you such course. I do conduct such courses. To know details of these training programmes, you may <link outdated-removed> .
All the best!
5th October 2015 From India, Bangalore