Action Details
Requirements and how-to articles for Vimeo's action:

Host a high-quality live stream for your audience. (Note: Live streaming is only available for members of Vimeo's Premium plan.)

You need this to get it done:

Stream Feed
In order to stream, you just need to connect to a camera and any RTMP-enabled encoder, which sends your live recording to Vimeo.
Each stream is limited to 12 hours in length, but you can host as many streams as you like.
Decide who can watch your live stream from the following options:
Anyone can see this video
Only I can see this video
Only people I follow can see this video
Only people with a password can see this video
Only people I choose can see this video
Hide this video from Vimeo
Only people with the private link
Hex Colour Code
You can customise the colour of your stream video player with a six-digit hex code.
Call to Action
You can add calls-to-action to your live stream for your audience to engage with.
A poll requires a question and up to four answers to choose from. You can also set the poll up like a quiz, with one correct answer. You can have as many polls as you’d like per stream, but only one poll may be open at a time.
Once your stream is live, you can enable Q&A from the Live Preview page. Viewers in both your on-site and embedded live chat can participate in live Q&A.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Vimeo - Live streaming
Official information about live streaming on Vimeo.
Vimeo Blog - How to maximize audience engagement with live video
Official blog post with live streaming engagement tips.
Vimeo Help - Vimeo Live overview
An official overview of Vimeo's live streaming features.
Vimeo Help - Live Polls and Q&A
Official information on the poll and Q&A features available for live streams.
Link missing here or found errors? Improve How-Tos