Grab your chocolate! :) It doesn't matter what colour it is. White chocolate burns easier, so you have to be more carefull with it. Chop the chocolate (if it wasn't already) in tiny pieces so it'll melt faster.
Grab a pan and a bowl. I like glass bowls more because you can see through them. Get a bowl that's bigger at the top than the pan itself is so that it won't touch the bottom, Fill the pan with water but let it NOT TOUCH the bowl.
Make sure the bowl doesn't have ANY water in it. When chocolate comes in touch with water, it won't melt properly. Put the chocolate in the bowl and put the bowl in the pan. Turn on the fire and make sure the water doesn't boil. If you're using a bowl you can't see through, and you wanna see if the water boils halfway, move it fast so that the evaporated water doesn't come in touch with the chocolate. Be carefull of people who might be behind you though! :P
When the chocolate is a bit melted, grab a spoon and move it a bit.
Keep it on the fire untill the chocolate is all melted and then it's ready to be used for whatever you need the melted chocolate for. Be carefull though, both the bowl and the chocolate are quite hot!
Oh and by the way- I have tried to melt the same chocolate bar twice (means that I first melted it, then it got hard, then I tried to melt it again) but that didn't really work out, so you're warned if you wanna try. :P