help with query

>ambigous column name
That's because numderord exists in both odc and suplementos tables, and T-SQL doesn't know which one you want to insert, and won't assume for you.

INSERT INTO suplementos(numdeord)SELECT DISTINCT odc.numdeord FROM odc LEFT JOIN suplementos ON odc.numdeord=suplementos.numdeord WHERE suplementos.numdeord IS NULL

or

INSERT INTO suplementos(numdeord)SELECT DISTINCT suplementos.numdeord FROM odc LEFT JOIN suplementos ON odc.numdeord=suplementos.numdeord WHERE suplementos.numdeord IS NULL

You need to specify where you're getting numdeord from:

INSERT INTO suplementos(numdeord)
SELECT DISTINCT odc.numdeord
FROM odc
LEFT JOIN suplementos ON odc.numdeord=suplementos.numdeord WHERE suplementos.numdeord IS NULL

Try:

INSERT suplementos ( numdeord )
SELECT odc.numdeord
FROM odc LEFT JOIN suplementos
    ON odc.numdeord = suplementos.numdeord
GROUP BY odc.numdeord
HAVING COUNT( suplementos.numdeord ) = 0

Saludos