Sometimes you can get a used keyboard from an online reseller's marketplace to start your lessons, and that's great. What's not great is sitting in a chair and placing your keyboard on a kitchen table or desk to play. Invest in your lessons by getting the proper instrument equipment to assist with posture and technique early on - you'll be thankful later.
Single braced is designed for medium to full size keyboards, violins, etc. Double braced is for heavier full-sized keyboards and other gear.