Does anybody here knows how do you make an application which will stream live videos/audio? For example: Skype, WhatsApp etc.
What technology do they use? May be some link in the comment will help me..

Stream video via https://en.m.wikipedia.org/wiki/... I would suggest using UDP/QUIC https://en.m.wikipedia.org/wiki/... because you don't want to bother resending TCP packets on live video.

Might be worth to check out the technical specs on the new video calling feature from Signal (private messenger). Entirely open source and doesn't lag a bit for me even with a crappy connection!

Check out WebRTC stuff. New standard that enables p2p streaming using plain JavaScript and web browser

@rastapasta42

Go for webRTC

Its awesome stuff. Our team has developed applications using this technology with MEAN Stack.
Faster and robust application development experience.

It all depends on what platform you are using for your live stream and for what purposes. I use Discord for this and find it the best place for streaming. But if you have not yet decided on a platform for this, then you can turn to this source https://livestream.studio/discord/ Here you can find useful information not only about using Discord, but also other platforms, as well as advice on choosing software and accessories for your live stream.