You need a motif. You need the basematerials for those motifs. E.g Obsidian Moonstone, Bone, asf.
Then you need to invest some of your Lootdrop Items and Research attributes, which are connected to gemstones. Depending on what kind of Setcrafting Place you are at: You need either 2, 3 or 5 Traits to craft an Item. Depends really.
So then you head and gather Ore Metals and refine them into Ingots. And then you go to your favorite forge and craft your Set together.
In regards to Motifs, you already have one on the class you made, your own races Motif (style).
So you can technically craft without Motifs, as long as you have everything else.
If you are not brand-new to crafting, then the most likely explanation is that you have not researched enough traits to create an item of the set belonging to that station.
The crafting station in the Earth Forge is for the set Kagrenac's Hope. This set requires that you have 8 traits researched for a particular item before you are able to craft the item with the bonuses for that set, meaning that if you want to create a 1-hand sword of Kagrenac's Hope, you would need to have completed research on all 8 traits for the 1-handed sword. Researching 8 traits on a single item takes about two months, and that time can be reduced through crafting passives (30% iirc?).
At this point in the game, nobody has 8 traits researched on any item.
Personally I have 2-4 weeks left before I unlock my 8th trait for Bows, Healing staffs, and Fire staffs, but I only have 3-6 traits researched for most items, and I am a very dedicated crafter.
If you are not brand-new to crafting, then the most likely explanation is that you have not researched enough traits to create an item of the set belonging to that station.
Yes, that was it amdaak89ub17_ESO also figured out. Thank you everyone for helping me grasp this.