Buying a bicycle doesn't have to be hard or difficult to accomplish. Despite what others say, it should start with the type of commitment that is required to engage in an activity that will blow your mind. However, how much money you want to invest is a decision you have to account for way before you visit a store and start talking to all the cycling savvy folks. Options are diverse—mountain, road, hybrid, or city/commuter— but not at all limited as many brands and accessories are available for each one. Next, think about what are you going to do with it. Consider things like what kind of terrain you'll ride most, what distance you want to cover, and what you want to accomplish.
Urban commuters actually have it easier than mountain bikers as they will ride most of the time on pavement. One item is similar between all kinds of urban bicycles: speed. They provide a smother ride, have more accessories and provide utilitarian features that make them multipurpose time machines. Usually they require lower maintenance and can be repaired almost by anyone with a slight inclination to mechanical maintenance.
Another good piece of information before making a decision is your location. Pick the right bicycle for your daily commute and for the weather conditions you will experience more often. Fenders will be required in cities where it rains and fat tires where it snows. Aluminum frames are better suited for areas where temperature can raise above 40 degrees Celsius and frames with disc brakes in cities with plenty of uphills and downhills.
Stick with your budget! Don't get carried away and get your bike fitted to your anatomy. Nowadays most bicycle components are very reliable and the quality of them are fantastic. In most bicycle stores, the products carried are actually tested and tried by their own sales people and technicians. Listen to their advise but remember that you don't have to buy the most expensive items in the store and you don't have to walk out the store with a bicycle you are not in love with.
Pick a color that motivates you to bike! It may sound silly but there are studies that suggest that wearing and riding a bicycle in the colors you love, improves your health, motivation, mood and even help you lose weight! —I know, mind blowing—so, think about this when picking your cycling socks, your helmet, your gloves...everything. Don't follow the trend! Become one!
Welcome to the cycling community! Hope to find you on the road some time.