You get access to the blacksmith after reaching level 90.
There are several ways to get to the blacksmith: either click the "Obscure Pommel" of the glimmering sword next to Shakes in the weapon shop or click the weapon shop menu button twice.
The blacksmith offers six services (socket upgrade, attribute upgrade, dismantling items, change look of item, gem extraction and swap runes) that cost a certain amount of resources (metal and arcane splinters).
To use a service, drag and drop an item from the inventory onto the respective area. Items in your backpack can be accessed via the right-click context menu which is essential for changing the look of an item and extracting gems.
How much metal and how many arcane splinters you have is displayed under the four functions of the blacksmith.