CRM OnPremise 2015 License Details

Hi All,

I would Like to know about MS Dynamics CRM 2015 On Premise License Details,

1.If I have 1 Basic License how many users can use it and how many developers .

2.If I have 1 Professional License how many users can use it  and how many developers.

3.Also if i have one admin account now many people can login with same credentials at a time.

4.whats the difference of Basic and Professional License.

I was not aware of Licensing related so expecting some simple and clear explanation.

TIA