See also the official documentation:
Help Center > Members Manual > Understanding Groups.io accounts > Logging in to your account
How to get online at Groups.io the first time
At Groups.io using your browser on ANY internet enabled device with a browser:
Note: "Click" can mean "Tap" on personal devices
- Use this link in your browser https://groups.io/login
- On that page click on the button that says "Email me a link to log in."
- When you get the email on your device, click on the link or copy and paste it into your Internet browser and go there. You are officially now "IN."
- The first thing you should do is to Bookmark that page so you don't have to go through all of the above again.
- The second thing is to set up/change a password for the same reason:
- Click on your identity in the upper right of your screen.
- Click on Profile in the dropdown.
- In the box next to the word Password, enter a new password.
- Click on the Change Password button.
- Near the top of the screen you should see something like "Your Groups," which you should click on.
- Click on the name of your group.
- You should now be at the Messages.
- Bookmark this page on your device.
That should work for anyone on any device.