Proxy connection

Hello,
(I’m n00b about browser extension and I’m trying to study it)

For test I’m developing an extension with Proxy, for example, for some website my extension have to use an external web proxy…

But I have basic problem I don’t understan how create a connection with an external proxy…
Someone can help me about it ?
I found https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/proxy but there aren’t examples…

Thank you for your time.