HI Suneel,
KNA1 table is used for the Customer master table.
Ex. When we have sale some material to any party or company then to maintain data against party then we create the customer code using XD01.
KNB1 table is used for the customer and company code.
Ex. Means we have multiple company code in each organization so for which company we the Customer is open that we see in knb1 table with the combination of Company code.
KNC1 :- Table used for KNC1 is used for store the Debit / Credit information about the Customer.
Regards.
Suneel