What is the difference between "The Ale", "The Brown Ale", and the "Mild Ale" beers? The colour seems more or less the same so, is it the taste that normally is different or is the level of alcohol present on the beer?
Beers (ales and lagers) are broken down into many, many different styles based on how they are brewed. Most beers have only 3 or 4 different types of ingredients. Malt, water, yeast, hops and sometimes fruit or herbs. While there doesn't seem like there can be a lot of variation, there are almost an infinite amount of ways to combine these ingredients. For the specific beers you mention, Brown Ale and Mild Ale are very similar styles. I'm not sure what you mean by "The Ale".
English-Style Brown Ale Style Family: Brown Ales The English-style brown ale ranges from dryer (Northern English) to sweeter (Southern English) maltiness. Roast malt tones (chocolate, nutty) may sometimes contribute to the flavor and aroma profile. Hop bitterness is very low to low, with very little hop flavor and aroma. Known for rich and advanced malt aroma and flavor without centering too much on hops, the English-style mild is extremely sessionable and food-friendly.
English-Style Mild Style Family: Brown Ales Malt and caramel are part of the flavor and aroma profile of the English-style mild while licorice and roast malt tones may sometimes contribute as well. Hop bitterness is very low to low. U.S. brewers are known to make lighter-colored versions as well as the more common “dark mild.” These beers are very low in alcohol, yet often are still medium-bodied due to increased dextrin malts.
If you want to dig deeper into this read the Beer Style Study Guide