Truing or dishing the wheel is pretty easy. First get yourself a spoke key ( http://www.tartybikes.co.uk/product.php?product_id=2010&category_id=31 ). Then spin the wheel slowly in the frame and note which part of the wheel you want to move across. If the whole wheel needs shifting left or right this is even easier, you'll be adjusting spokes all the way around. Next have a look at the spokes in the section you want to adjust - alternate spokes come from different sides of the hub. If you tighten alternate spokes (all coming from the same side of the hub) it'll pull the rim in that direction.
To tighten a spoke, use the spoke key to rotate it anti-clockwise when viewed from the centre of the wheel. This pulls the spoke nipple up the spoke itself, pulling on the rim. Do an eigth to a quarter of a turn at a time, no more than that. To dish the whole rim, start at the valve, rotating alternate spokes a 1/4 turn until you get back to the valve again. If it needs more go round again, but don't be tempted to do more than 1/4 turn at at time. You can also loosen the spokes pulling the rim the wrong way by a 1/4 turn, but I don't normally find this necessary unless things are getting very tight.