Answer : - Online courses: There are a variety of online interior design classes you can find on websites such as Skillshare, Etsy and Amazon. A few free classes I've found in just a quick search were at Skillshare--"Introduction to Interior Design," "Commercial Lighting for Architects and Interior Designers," and "5 Ways to Make Your Home More Beautiful." On Amazon there was "Interior Design Masterclass Redesigning Rooms That Work." And finally, one Etsy course offers the whole package with certifications by the Royal Institute of British Architects. - Books: Perhaps most easily accessible is through blogs like Apartment Therapy which offer guides on how to redecorate your home on a budget.