Yes entropymancer is right, FAQ is the first place to check.. As you see, the FAQ links a thread that is a sticky in the information subforum, so also do check stickies in each subforum for relevant information.
Regarding weighing, as entropy said, you need a scale. A 0.001g (milligram) scale is good but you can definitely get by with a 0.01g (10mg) scale. Im sure you can find them very cheap, local dealers, ebay, etc