THE KEYS ON THE OBOE are operated by both hands. What the keys do is alter the length of the tube of the oboe. Obviously, just looking at an oboe-player at work doesn’t show this – but it is not the tube that makes the sound so much as the air being blown down it. So when a key is opened (by opening its metal covering or removing the finger over it), it affects the distance the air has to travel. This then alters the pitch of the note. This is true of all woodwind instruments.
Over the years the key system has become more and more elaborate. On a simple woodwind instrument such as a recorder, all holes are covered by fingers. But the oboe is too long for this, and the demands made on it since the early 19th century (and occasionally before) have necessitated adding keys to enable all the notes of the chromatic scale to be available.
Of course, the keys have altered the sound a bit over the years, as have the types of wood used; so while the modern oboe can play music impossible on earlier oboes, it no longer makes the sound that Mozart or JS Bach would have heard.