Sadiep's instructions are very good :D. Ganache isn't really a "recipe". It's a *process* and in order to make it you have to understand the process.
Cream is an emulsion. Fat floating in water.
Chocolate is also an emulsion. Fat floating in water.
Chocolate also happens to be solid at room temperature and cream is liquid at room temperature. If you can convince cream and chocolate to mix together, they can become semi-solid (which means a little of both) and you get room temperature ganache.
Warm ganache is kind of like melted liquid candle wax (I iknow that not the most flattering description), while cool ganache is more like the soft drips of wax you can roll between your fingers. In order to pour ganache, it _has_ to be warm. Cool ganache is spread like frosting.
The reason why any of this matters is it communicates clearly what's "wrong" with your ganache. If it's too soft...it has too much liquid (ie: cream). If it's too hard, it has too many solids (chocolate). If it's curdled-looking and won't blend...you broke the emulsion (the water and fat have separated). If it was runny enough to pour before you let it settle and now it's cool, if you _gently_ reheat it it will be pour-able again.
I found this video on Youtube that's a pretty good example of making ganache:
"When" to pour the ganache is a bit of a challenge. I let my bowl sit on the counter cooling for about an hour. It needs to be warm enough to still be melted, but cool enough to leave a thick layer on the cake :D. If you want a very thin layer of the ganache, pour it right after it's all mixed and incorporated.
I don't know what Wilton melts are (I don't use Wilton products), but as sadiep said, you absolutely want to use real chocolate. It doesn't have to be the highest quality (I've made ganache with regular store-brand chocolate chips), but don't use candy that happens to be chocolate-flavored.