What is the best thing to do for a younger manager you just finish his studies or his course?

Start by gaining experience through Internships and smaller job opportunities as a way to build up on your resume and portfolio. Make yourself look attractive to job seekers and recruitment agencies. Learn as much as possible in the spare time about the market you are interested in working in. The extra knowledge gives you an edge during the recruitment process especially during interviews. Also connect with more people in your network as that is highly integral to your development as a person. You may also explore options to do your Masters in due time.

Whatever he thinks is best for his career.

Sometimes it is difficult to find a job . Volunteering  ,attending seminars and trainings  would help a young graduate person to gain experience.

Get a job.  Gain some experience.  Look to move on/up after a year or so.

I fully agree with the answer been added by EXPERTS....................Thanks.

Actually a young fresh graduate managers can't find difficulty to find a job that match to their  field of expertise if in their  college studies performance  was stunning and well develop skill. In college there's a lot of programs / subjects, to practice for the perfection of career. However, some companies always look an excellent  students ( in their4th level before  graduation ) in universities to fill in their vacant position and  to work with them. Then after graduation,  companies will hire them. And most of the universities are ties up with companies and that they can recommend their  excellent student to work. In short everyone should take their career seriously and should have stunning performance and  skill during  their  studies to get  job easily right after graduation.

In case of those graduates that still hunting a job I think they needs back-up such as politicians, well-known and popular people recommendation ( this is  a trend today ) while waiting they can volunteer and take seminars  is a plus.

Get your hands dirty and gain significant insights for the job. This will make you a respected manager in the future. W/o the respect of your people and their confidence in you, it doesn't matter how many diplomas you cane show them.