1. PRICE RANGE
The first step would be to figure out what price range you're looking for. DSLRs usually begin at around $400 for the camera body and lens. If you're a newbie to DSLR cameras, I recommend googling "entry level DSLRs" - that's what I have! You might find a list of recommended cameras, usually ranging from $400-$600. Some come with "kit" lenses and some are just the camera bodies. If this is too high for you, look into buying used cameras or high quality cameras that aren't DSLRs (my sister got a really nice one used for $300).
2. ASK FELLOW PHOTOGRAPHERS
There are so many different kinds of cameras available that you might not even know where to begin. One thing to do would be to ask a photographer you know. What cameras and lenses do they recommend in your price range?
3. LOOK UP REVIEWS
Once you've found a handful of potential cameras, google each one. I spent a few days just looking up reviews to help me decide. I also went into Best Buy and played around with the two cameras I had whittled it down to, and immediately liked one better than the other. It was like that feeling brides get when they try on "the" dress ;)
4. WHERE TO BUY FROM
My camera was sold at several stores including Target, Best Buy, Amazon, and a few small shops online. Best Buy and Target had a much higher price than Amazon, plus Amazon's warranties were cheaper and I got free shipping with Amazon Prime. For me, this was definitely the way to go. If you are interested in purchasing your camera from a small online shop you've never heard of, make sure to google that website to check if its fake or spam, especially if the price seems too good to be true.
5. BUYING USED
You can also buy your camera used. Places like Amazon, Craigslist, and Ebay are great for that. Here is a good guide on what to look for in person and here is a thread on what to be cautious of. (I opted not to purchase mine used because the camera model had come out several years ago and I wanted to be sure that mine wasn't already pretty old.)
I always recommend getting a warranty for your camera. Something this expensive is worth paying the extra $30-$70 in case of an accident! I bought a 3-year warranty off Amazon at a really great price and much cheaper than Best Buy.
This is all based on my experience with purchasing a camera. I hope it has helped you!