Wort is the name for the mixture of unfermented sugars and hops oils that every beer starts out as before it becomes beer. Wort production can be an increadably complex process if you are an all grain brewer or very simple if you are an extract only brewer. Many brewers reside somewhere in the middle and do partial mashes as required to get certain characteristics out of their beers. I occupy the space between a extract brewer and an all grain brewer so I will approach the subject from the stand point of an extract brewer because that is the easiest method and you can get fancier as you desire.
Wort is produced by using the natural enzymes in grains to convert their starch to sugar. It is a natural process that happens as a seed germinates as well, we just take advantage of the sugar before the seed germinates. There is a laborous process all grain brewers perform which effectively results in the liquid or dry malt extract brewers use. The end result though is relatively the same which is why extract brewers can produce beers which are just as fine as all grain brewers in most cases.
Aside from your yeast's flavor profile wort provides the majority of the characteristics of your final product. The first thing to consider in wort is the percent alchohol you want your finished beer to be. The most accurate way to do this is by taking specific gravity readings of your unfermented wort and fermented wort and the difference is the is the amount of sugar that has been converted into alcohol. For a beginning brewer however a good rule of thumb to follow is to take the total pounds of malt extract or sugar that you use, subtract two and that will be the approximate alcohol content. For example a recipie that uses 6 lb. of malt will yield a beer with around 4% alcohol content. There are other factors such as yeast attenuation which will influence your final yeild, but that rule of thumb works pretty well if you aren't picky.
The second consideration is how much body you want your beer to have. Body is what makes your beer heavy versus light. Body is NOT color, but they often go hand in hand. Typically the lighter the malt extract, which usually comes in three colors: light, amber, and dark, the less body the beer will have. If you wish to make a light beer that is full bodied we can use another method to help, but it will never have as much body as a dark extract based beer without significant work. It is not a problem to make a very dark light bodied beer however, so don't choose a dark extract just for the coloration. Choose your malt extract based on desired body with consideration for final coloration if that is an issue.
Once you have chosen the type and amount of malt extract, which is the vast majority of the sugar you are using, you can also choose to use a specialty grain to give your beer special qualities. Almost every beer you will make you will want to tweak with grains so it is good to learn about them now. Grains you use for your wort production can be malted or unmalted, enzymatic or not (though almost all are not), and highly differentiated in color. Grains are steeped like a tea bag in your wort water before you add the malt extract and give the wort both coloration and specific taste. You will select your grains based on the recipie you are using and you should take a look at my recipie section to get an idea of what kinds and amounts of grains are used for a particular style of beer.
Finally, once you have chosen your malt and grains you need to choose your hops for the beer. This section will eventually become its own because it is so important in brewing but for now you will have to make due with the short version. Hops provide both bittering, flavoring, and aroma to beer. Typically hops are added at three stages in brewing which corispond to its intended use.
After the boil is complete you need to chill your wort down to pitching temperature as quickly as possible. Pitching your yeast at a temperature which is too high can result in off flavors which may not be desireable. To do this there are many fancy devices but a simple method is to take your brew pot and set it in a sink or washtub full of ice water untill it cools. From there you can syphon it into your primary fermentation vessel and make sure you have 5 gallons by topping it off with cold or room temperature water.
That is a short stint into what factors choose your wort production. What follows are directions on how all your ingredients should be mixed and in what order during the wort boil.
Turning your ingredients into wort!