Knitting terms can be confusing..dk, aran, 16 stitches to 4", bulk, super bulky, gauge...There are many basic charts on the internet that will help you become more familar with the standards set by the Craft Yarn Council of America
http://www.craftyarncouncil.com/weight.html The chart lays out the different names used through the ages by different countries and the numbers that now go with them.
The term worsted originally comes from the 12th century weaving industry in Worstead England. It is also a term used for the carding of wool and the spinning of wool and the subsequent fabric made from it. Interesting but not relevant for the knitter who wants to know what size needles she needs and what yarn to buy.
In the end, its quite simple, its about creating a fabric that you like that will work with the pattern that you have chosen.If the pattern calls for a 4.5 mm needle and the fabric is too tight, then you are best to go up a needle size, and consequently if it is too loose go down. Making a swatch may seem silly or unnecessary, but it helps test the yarn you have chosen to see if it works and mostly importantly whether you like it. In the end its sillier to knit a whole garment to find out you don't like it or it doesn't fit.
