You can take Interior Design classes online and get your degree, but you cannot gain the real working knowledge of the industry without an internship.  Interior Design Internships are where you get the working knowledge and experience needed in this industry.  If you do good work and keep the customers happy and coming back for more, many Interior Design firms will keep you on if you so choose.  You will at least have the experience behind you to get a job at another firm and possibly even the word of mouth advertising from your clients to start your own Interior Design business.