I am fortunate in having several friends that are bee keepers and they give me their wax that i render myself.
The simplest method that I've found is to melt the cappings with water in an old pot that is used exclusively for rendering wax.
It must be over a very low heat so that the wax doesn't overheat. When it has completely melted, leave it to cool overnight and the wax will be in a solid disc on the top.
The impurities will be at the bottom and can be scraped off with a serated knife. Keep the scrapings to melt down for firelighters.
Repeat the process until there are no longer any impurities (slum gum) on the bottom of your wax.
I used to filter the melted wax through a muslin cloth but found this method easier.
Once the wax is clean enough, i melt it again without any water and pour it into mini silicon muffin molds which hold 25g wax when filled to the top.
For making a salve, i find four parts infused oil to one part wax the consistency that I like.