MBA/PGDM

Hey,
There are 3 major wings based on the kind of firm you work for/with:
1- Corporates
If you're straight out of college, you would begin with Recruitment, Salary Processing & Payroll, Designing Employee Offer Letters, and coordinating all other activities in screening the right candidates.
With some experience you could move into Designing the Training Calendar, Screening Training needs based on manager feedback and employee roles, getting in touch with training providers or designing your own programs, identify leaders early and try to put them through projects and learning activities to take up bigger positions later. This would also include employee appraisals, performance benchmarking, etc.
2- Agencies & Consults
There are plenty recruitment agencies out there who basically outsourcing the screening and testing portion of the recruitment process. They're bet is on having a large base of relevant people and ideally operate in particular sectors or specific profiles and rely more on the volume of applicants.
An MBA (HR) can easily enter at a Manager level who spends more time filtering applications and matching them with upcoming jobs as opposed to interacting with applicants and getting them on board (that's for an undergraduate to do)
3- Recruitment Process Outsourcing (RPO)
This has been the new addition to the kind of services an HR Professional can provide.
The basic idea is to have ready candidates - if an employee leaves your client midway and the client would have to spend time hunting another employee then an RPO guarantees a ready supply without any time wastage!
This is like an advanced version of a Recruitment Agency where you assume responsibility for the work and efficiency for each hire; also allowing a regular supply on time.
All 3 would require very different skill sets and commitment to understand how the business works and adapt to it.
Good Luck.