I have just started brewing my own beer and though I have made a few batches (3 to be exact), I wanted to know what categorizes a brew to be a beer (like Mead/Lager, Irish Stouts). Is it the hops/Yeast? I just would like to know so I can look up recipes as I start to play around with recipes of my own.
There are many different styles of beer, and it is generally accepted that beer is brewed from malted grain (in almost all cases at least some portion is barley), water, hops and yeast. The different styles get their flavors from the types of grain used, the varieties of hops, and the strain of yeast.
Note that mead is not beer -- it is brewed from honey, not malted grain.
The Beer Judge Certification Program is a non-profit organization that promotes judging at homebrew competitions. They have documented the major styles in Style Guidelines That is one place you could start to see the list of styles. The guidelines include suggestions for ingredients, but do not contain complete recipes.
The two main categories are ales and lagers. They are distinguished by the yeast strains that are used. Ale yeast ferments from the top of the fermenter and lager yeast the bottom, they also have many different characteristics such as flavor profiles and temperature requirements. Lager requires colder temperatures.