You can find live videos on Instagram very easily. If you are following someone who goes live then Instagram will send you a notification on exact time. You can join on direct click on notification.
You can find it in your app's home page. Open the app and you can see the live video in first circle of your all stories, if someone goes live. It's on the top of the home page.
You can watch other top live video in search section. Open it and you can see current live videos on the top. You can watch it there.