Articulation on the oboe means when to use our tongue to articulate notes versus not using our tongue (or slurring notes together).
To articulate on the oboe we use the "Tip of the Tongue on the Tip of the Reed".
What this means in actuality is the very upper tip of our tongue will gently meet the tip of the reed. Some people like to visualize it as the tongue going in between the 2 blades of the reed, while others visualize it as the tongue touching one tiny corner of the reed to stop the vibration.
The most important thing you should remember is that you should not physically feel your tongue hitting the reed- this means you're articulating with too much force. Your tongue should gently touch the reed, just enough to stop the vibration of the reed in between notes.