There is a much longer conversation about your eventual goals for the company and plans for monetization and hiring. However, I would keep it simple and form an LLC.
LLCs are relatively easy. You might be able to get everything done (or at least the forms submitted) by this afternoon if you start right now.
Forming a C-corp is much more involved and comes with a lot of hidden extra hurdles that aren't insurmountable, but they can be an extra drag on your time if you already hate dealing with the paperwork and other details. I'd look into a C-corp before you plan on bringing in other co-founders or investors or anything complicated like that, but in my experience they're not necessary at this stage.
And yes, you do want to form some sort of business entity for this venture. The chances of encountering legal trouble are relatively small, but if it does happen then you'll wish you had taken a few hours to at least form an LLC to protect yourself.