If you have an MBA, then you must have preserved textbooks or study materials from your course. Why not go through these very books that you studied earlier? Since you have read that text before, it will be easy for you to grasp. In contrast, material on web resources is scattered and may not be organized. The exception could be related to labor laws. Changes have taken place in many labor laws, hence you may not rely on those textbooks.
Practical HR Requirements
The actual requirements from HR are different from what you learned in your MBA. Your employers could expect you to be thorough with recruitment, payroll processing, and even statutory returns. This practical knowledge is not taught in an MBA. Notwithstanding this shortcoming, you can make a beginning now. Other things will follow.
Utilizing Forum Discussions
You may go through the discussions on this forum itself. Every day, even if you spend an hour reading various queries, it will give you a lot of practical knowledge.
All the best!
Regards, Dinesh Divekar