How to give solution for cases ?

can anyone provide full docs for cases& solutions?

where is sfdc sample projects available with source code ? and  what is the functional flow of salesforce?

thanks in advance 

can any one say plz    Where “database.query” will come?

How many ways we can do  mandatary the field ? can any one say plz ....thanks in advance 

How to give solution for cases ?

can anyone provide full docs for cases& solutions?