We use water baths to melt ingredients to avoid over-heating them; by insulating our melting ingredients in water we ensure they never pass 100°C/212°F. This helps prevent scorching our lovely ingredients.
I like to make one by placing a small heat resistant glass measuring cup in a small saucepan that’s got about 3cm/1″ of water in it. I’ll place that on the stove over medium heat. The water will heat up, and will take the ingredients with it. If your saucepan has a thin bottom you should consider using a small double boiler ring (basically just a wire circle) or a silicone mat to separate your measuring cup from the bottom of the pan.