You need to find coal pretty quickly if you want to make any headway in Return to Moria. As with most survival crafting games, you'll use this resource to fuel your forge and furnace, which in turn allows you to craft tools and weapons. Coal is also required to build a fire if you want to bed down away from camp.
You should find a few pieces of coal in the first camp you come across, so you won't need to go looking for this resource straight away. As soon as you want to start making more than basic tools though, you'll need to start sourcing it yourself. With that in mind, here's how to find coal in Return to Moria.
Return to Moria coal: How to find it
There are two ways to get coal in Return to Moria. The easiest way is to make it at a Stone Hearth but this is also the most expensive way, costing you 25 wood scraps for every piece of coal you make. Wood scraps are pretty plentiful and you can find them almost everywhere around you by breaking barrels or other wooden objects, or by just picking them up off the ground. Still, it's going to take a lot of foraging for very little coal. It's also worth noting that you can also occasionally find coal on storage pallets near ruined forges.
With that said, the better way of acquiring the resource is by mining it, and you only need a simple pickaxe to do so. I found a large vein of coal in the Elven Quarter, near the second broken camp and close to the wall where you mind your way through to the area. As each world is procedurally generated, it's likely to be in a different place for you, but it's fairly easy to spot as it's black with orange edges. Check the screenshot above if you need help with knowing what to look for.
As a point of reference, the coal vein pictured got me around 60 pieces of coal, so it's a far more efficient way of acquiring this material. And it means you won't have to waste your wood scraps needlessly.