Error: Incorrect usage of UNION and ORDER BY
Wrap the selects into parentheses

(SELECT DISTINCT CONCAT (MONTH(`Date`),'-',YEAR(`Date`)) from wp_result_plugin WHERE Bet=2 AND month(`Date`) = EXTRACT(month FROM (NOW())) ORDER BY MONTH(`Date`) ASC )
UNION 
(SELECT DISTINCT CONCAT (MONTH(`Date`),'-',YEAR(`Date`)) from wp_result_plugin WHERE Bet=2 AND month(`Date`) ORDER BY MONTH(`Date`) ASC)