How do I make my cash only business legit?

I do not know the first steps to take to make my business legit. I have just been buying used items at thrift shops, yard sales, storage unit auctions ect. and turning around and selling them for a small profit. It started out just putting a little extra money in my pocket. Then I lost my job and I was able to put a lot more time into this. This isn't going to make me rich but I will probably not have to work for anyone else again! Most of my business is cash only since I buy most of my stuff from an individual person and I sell it on craigslist or at my own yard sale. I have very few papertrails but I would like to make my business legit as far as taxes go. Does anyone know how I would do this?