Our teacher gave this to us:
Public sector business organisation --> public organization --> public enterprises --> central ministry and municipal.

(Public enterprises has been divided into two parts. One being central ministry, other being municipal.)

Has anyone got any idea what this is? Any help will be largely appreciated.
Or teacher says nothing. And gets angry when asked about something.

Look at this internet explanation of the differences between Private and Public Sector.

Difference Between Public Sector and Private Sector (with Comparison Chart) - Key Differences

The best way to examine a huge problem is break it down to smaller, easier to handle components. Research the components and how they work, and the bigger picture becomes clearer.

I know these things. But what do these single arrows mean?

It's an organization tree (Or referred to as an organizational CHART) if you mean your original post. The top is the whole, and it breaks down into its parts.