Start with the first join and see how that goes

SELECT TOP 100 *

FROM S_OPERATION, S_FILE_NUMBER FNUMBER

JOIN S_CUSTOMER SENDER

ON S_OPERATION.SENDER_ID = SENDER.C_CUSTOMER_ID

Are you trying to join 2 tables S_OPERATION and SENDER?

Then this should work

SELECT TOP 100 *

FROM S_OPERATION AS O

INNER JOIN SENDER AS S

ON O.ENDER_ID = S._CUSTOMER_ID