I've been thinking a lot about the different steps I need to take to legally start selling cakes out of my home. But what is the first step? To have a legal name??? How do I go about doing that?

Any help is really appreciated!!!

You are very lucky to be in a state which allows you to do that! Here is a link that should get you started:

http://www.mass.gov/agr/markets/specfood/selling_foods_made_in_your_farm_kitchen.htm

Best of luck.

Make sure the name that you choose to use isn't being used by anyone else. Some people think just because the name isn't being used in their area it's still okay to use the name...then face costly legal consequences later down the road. IMHO, it's just not worth it. Choose a name that is unique and consider trademarking it if it's something you plan on sticking with. Check with uspto.gov/trademarks and do a basic search.