Rebates - Config/Set up Question

Hi experts,

While setting up rebates I have some trouble mapping following:

1. Account determination --> The condition BO02 is acct key ERB and accruals key ERU

In account determination for ERB where should I enter the account number (in which G/L account column first or second) ?

Similarly for  ERU where should I enter the account number (in which G/L account column first or second) ?

2. When entering amount in condition record (VBO2) what is the difference in Rate and Accrual ? Should the rate be not same as accrual ? Do we not pay what we accrue ?

Thanks for reading !

SAP, SD, OTC, Rebates, R/3, Billing