oooooooooooooo ok, Now I get what happened.
Yeah you would need to knit a swatch first (about 5" by 5") don't cut the yarn from the ball or skein but measure the little square in the middle not by the needle because then it's either all bunched up or all spread out. You won't get an accurate gauge that way. When you are done measuring your swatch, frog it (rip-it out) and rewind the yarn and THEN go for it.
O yeah, and doubling the yarn just means that you knit two strands of the same yarn as one strand.
Another thing I have learned is that the needle size on the ball isn't necessarily the only needle size you can use with a particular yarn. It's just the basic needle recommended by the manufacturer. Usually a designer will use a needle size that she has determined is best for her design. You can use the needle size on the ball to figure out the weight of the yarn though.
1-3 is usually fingering or sock weight
3-5 is usually sport or dk weight
sometimes dk can even be taken up to a size 7
7-9 is usually a worsted or aran weight yarn
anything larger is bulky, superbulky, chunky and novelty stuff.
But if you want to accurately find the gauge of the design you should really make a swatch. The pattern will usually tell you if it's on stockinette stitch (knit's on one side, purls on the other)
or if it's in the pattern stitch. Do what the pattern calls for.