Oracle's EXPLAIN PLAN can be used to display the query plan - steps that the database will use to execute the statement. Even though your statement is not a complicated one, you can see that the database will use an index (PK_x_table) when accessing the row you want to delete.
EXPLAIN PLAN is usually used when 'tuning' the SQL statements - making changes that would result into the statement being executed more efficiently. This is actually a vast and somewhat complicated area of expertise, but if you want to get better understanding of it, you might start with
this documentation, for example.