One of the most puzzling aspects of online lessons is how to get the optimal set up so teacher and student can see and hear what they need to. 

For the teacher, the most important input is the sound. Adequate sound quality is necessary to be able to provide timely and accurate feedback to the student. It is not necessary for the student to have an external microphone, although that may help. A good internet connection will go a whole lot farther to ensuring the teacher gets good audio quality. It may help to ask others in the house to limit their online access during a streamed lesson. Headphones or earbuds can help improve the sound quality received by the student. Headphones can have a better quality than the built in speakers of a lot of devices.

The second most helpful input for the teacher is the video. The quality doesn't have to be great. Music is experienced primarily by hearing after all! But visual aid can be helpful for a teacher to pin point the problem. The most helpful view is therefore one that is slightly above the keys looking down. This could be an overhead view, or a side view with a downward angle. Something like this is perfectly acceptable:  

I normally loves to see the student's face, but with an online lesson the most important view is of the keys and hands. I will shift the view to the keys if necessary to demonstrate something, but otherwise, will primarily let the students see a smiling face. 

The set up itself can look so many different ways depending on the device used and what the student has on hand. In the long term, the student may find a few gadgets a worthy investment to improve the set up.

If the devices used to is a phone or tablet, any way to prop it up with a view of the keys would be fine.   

Here a phone is propped up using an open frame music stand. Alternatively, a phone or tablet could be connected to a tripod using a special mount. Something like this phone mount for example. Or this tablet mount.

A music stand with an adjustable slant can be used to hold a laptop. (Note, I don't recommend using a non-adjustable music stand as pictured. It is really unstable, but with a lower slant or slope more like a table, it would work just fine. Something like this where the angle is adjustable would be much better.)  

Using a separate webcam is not necessary, but if you wanted to use one, you could set it up on a tripod to give an overhead view. My webcam is compatible to connect direct to a tripod without an additional attachment.   

Although the view is not as ideal, a laptop on a side table using the built in webcam can work okay.  

Hopefully these different setups can give you ideas on what will work for you! None of the items I have linked in this tutorial are ones I can personally recommend, but hopefully they give the right ideas so you can find what works for you!