It is really simple!
1) Capture anything you want to share with a screenshot, a GIF or a video recording:
2) Paste the link in any Slack channel or private conversation you want
Summary: CMD + Shift + 5 to take your screenshot then CMD+V to paste it in Slack.... who needs words and long explanations anymore?
Note: To be mindful of your data security, password protected links won't unfurl in a Slack conversation