Speaking as a long time ActiveRainer, and as an "Ambassador"...  unless you anticipate a good Following, the "Groups" are probably not going to provide you with any SEO or ROI.  There are a few exceptions (e.g. Bananatude), but in general the Groups don't get much traction.

     Having said that, follow the tips from BLiz aka Liz and Bill Spear and start a Group.  It only takes a couple of seconds to post to your Group..   Just be sure to monitor and moderate it!

Esther, As far as the how to part, go to top menu bar, select Resources, then Groups, then the bottom left of the page is START A NEW GROUP, set up the purpose of the group, etc.

After that, invite people, promote it, etc. and try to build it up.

See Liz and Bill Spear and Fred Griffin for tips.but as others have said interest in groups has waned over the years.  Good luck.

Technically Bill Liz and Bill Spear give you excellent advice.

Fred Griffin offers additional insight. 

Bill gave you a good answer. There are so many groups on AR even after many were weeded out because of limited use. I think promotion is key, and it should be something with broad appeal

Fred is right....and make sure you follow Fred.... he gives the best guidance....

I like Fred Griffin and Liz and Bill Spear 's advice.

What exactly is your area/expertise?

Liz and Bill Spear have the answer

You have some excellent advice already and it is true that interest in groups just doesn't seem to be what it used to be.

You're getting some great advice from a lot of very good members. I too have started a few groups and as other have mentioned have had very little traction. In fact sadly I rarely even monitor them any longer.

The one thing that will really thrust you into the mainstream of the AR Community is participation. Blogging, asking and answering questions. Liking and following others. They all get a lot of traction and will start building momentum quite quickly.

In fact I'm now following you!

That is kind of something in the older days. If you really like you can contact those in your area that you are forming one.  Many have dropped out over the past.  

Probably not worth your time, just utilize the localism box when you post.

Thinking the Groups have lost their mojo, and not many are visiting.  

Fred has a good answer.

Esther Preston you have lots of suggestions. 

The newest generation of ARers know very little about Groups . Be careful others don't use it as a dumping ground for their MLS stagant listings !

Be encouraged....you just took the first step

Form Facebook groups. Do not waste time with ActiveRain groups.

parked and reading

These days we do not post to many groups.

Looks like you have the answer here. Good luck!

Esther Preston many group admins are enthsiatic in the beginning. Just make sure you invite people to join this group and keep it active!

Starting a group - you already got the answer for that.

hmm, it looks like the right answer was already given

You can get great advice here! 

Looks like Bill of  Liz and Bill Spear has got you covered on this. Not much else I can add to this that others have not already commented. 

I did once and it was easy.  But when I tried to figure it out tonight, I got nowhere.  I'd email Bob Stewart and he'll probably be able to make it very easy.  

Oops!  I didn't scroll down far enough on the page.  There is a little icon there and it should be pretty simple.  Good Luck!