Look for a way to reference a SharePoint group in my workflow. I want to set a variable equal to the group. Not sure how to do that?
in my Visual Studio workflow I just reference either the group's name as a string or the groups ID.
Go into your workflow in SharePoint Designer (assuming 2013 as you didn't specify), add an email action and set the desired target (To/CC/BCC) to whichever group you'd like from the 'Select from existing users and groups' list on the left and hit add. It should email the group directly. No need to involve a variable in the equation.
If for some reason, you really wanted to, you could add a variable and then use a web service call to one of the REST services to get the user's email address as a string and then assign that to a variable, but that's needlessly complicating things.
A quick visual tutorial can be found here.