This article assumes you added NDI to your Open Broadcaster Software (OBS) and also that you know how to run a live webinar with OBS. If not please read these first.
Fire up your OBS and Skype app! It's time to get productive :)
To follow this tutorial and test, you are going to need at least access to two skype accounts. You can open one Skype account on your laptop and another on your phone. For delivering webinars with an actual guest you just need your own Skype account.
So first, go to your Skype app, call your other presenter. Or in this case, I am going to call myself on another skype account.
Once you do that, go to your settings by clicking on the "..." icon. then go to "Calling". Click on "Advanced Option" and turn on "Allow NDI® Usage".
After that, go to your OBS app, in "Sources" click on "+", and you will see a number of options. Choose "NDI® Source".
Once you do that, you will be able to add a name, to differentiate between different sources. In the next screen, from "Source Name", choose the one that you want to broadcast/stream. In this case, I am going to add myself (the cartoon pic and in the selection, referred as "Local") and the guest both (the slide and referred as "live:skypeusername").
In the "Mixer", you will now be able to control the volume for all the sources that you just added.