Interpreting a formatted execution plan requires practice and often some degree of judgment. However, the following fundamental principles guide the interpretation:
SORT ORDER BY
TABLE ACCESS FULL CUSTOMERS
TABLE ACCESS BY ROWID EMPLOYEES
INDEX RANGE SCAN EMPLOYEE_BOTHNAMES_IDX
Here, the indentation level of the outermost access determines the precedence of the execution. In this Explain Plan, the most heavily indented operation is the index range scan of an EMPLOYEES index. However, this operation is combined with the ROWID access of the EMPLOYEES table. Therefore, the CUSTOMERS access is the first step executed.