Can someone explain to me how rookie salaries work in the MLB?

I think that all rookies have base salaries until they are eligible for arbitration or FA, but my question is:

How much is this salary?

How long until they are up for arbitration?

When does the arbitration clock start ticking? For example, if we bring homer up this year, does that count as a full year? or how does this work?

Thanks in advance.