Can someone explain me the difference and usage of Best Practise Packages?

Hai Friends,

I am new to SAP product development based on sap best practices.

I need clarification on the different cases and usage scenarios of Baseline, industry and Cross-industry packages in SAP BestPractice.

My Doubts:

<b>1) In which case we use which package?

2) If Baseline package and Cross-industry packages are common to all industries what is the difference between them?

3) Is there any need to use baseline package in all solutions?

4) If we use Cross-industry or industry package, we need baseline package or not?</b>

Could anyone clarify my doubts by explaining it in a simpler way?

Regards

Karthik D