Dear Pradnya,
If you are MBA, then you must have preserved textbooks or study material of your course. Why not to go through these very books which you had studied earlier? Since you have read that text earlier, it will be easy for you to grasp. In contrast material on web resources is scattered and it may not be in a organised manner. Exception could be related to labour laws. Changes have taken place in many labour laws, hence those text books you may not go through.
By the way, at the actual requirements from HR are different what you learnt in MBA. Your employers could expect you be thorough with recruitment, payroll processing and even statutory returns. This practical knowledge is not taught in MBA. Notwithstanding this shortcoming, as of now you may make a beginning. Other things will follow.
Secondly, you may go through the discussion on this forum itself. Everyday, even if you spend an hour in reading various queries, it will give you lot of practical knowledge.
All the best!
Dinesh Divekar