They have made changes lately that make it easier. Go to the group via the link. Press join group. You then have to make a profile or pick one you already have. Mostly this is just your email address.
Fill in the spam bot trap - by entering the letters and numbers that are in the fuzzy box and then press join. I will then accept the request (fairly quickly unless it is night time here) and there you have it.
It lets you customise your settings but don't worry The default is to get all group mail and I can't see there being a real lot.