When you are first added to the groups.io site as a subscriber transferred from Yahoo, you have no password. Same thing happens if you join by sending a message to "firstname.lastname@example.org". To log in and set a password, you enter your email address (which is your login ID) and click the link that says "I have no password". You will be emailed a message that contains a link that, when clicked, takes you to groups.io as an authenticated (signed-in) user. Now you can click on your name (or email address) in the top right corner, select "Account" and you will find a bunch of options for your groups.io account, including setting or changing password. You can also set preferences and other identity options.
For subscription settings that are specific to individual groups (like email@example.com), click on the "Your Groups" icon at the upper left of the page, select "alfaseeya" and then click on "Subscription" in the left-hand column near the top. Here you can change "Membership" and "Group Profile" options (these are tabs across the top of the page). In "Membership", part-way down is a heading "Advanced Preferences" where you can also add alternate email addresses from which you can send messages to the group. There are lots of other options as well. Just browse through them. The option to add a signature to email and web posts is also there.
I also encourage you to set a "Display Name" under "Group Profile" across the top (then select "Edit Group Profile" and enter a display name). In my case, my display name is set to "Dave Rypma - 2006 SYG #4078".. That information is at the top of EVERY post that I send!
Any questions, just ask.
-- Dave Rypma 2006 Alfa Gold #4078 VE3HTC / VE3DTR