I'll try to explain the basics about Enchanting here.
After selecting the item you want to enchant and clicking the "Enchant" button actions you'll be presented with this screen.
1. Primary Modifier: It's the category. You'll choose which body part, type of attribute or, in this case, type of fetish you'll be looking at. After doing that move to the next step. Don't worry about misclicking, the only step you can't undo is the last one.
2. Secondary Modifier: Here you'll choose precisely what you'll enchant. Food items items will have the body parts under the chosen category you can modify; drinks and weapons have the attributes; clothes both and special effects. After choosing what you want to change move on to the
3. Boost/Drain Spectrum: Here you'll decide what is being done to that body part/attribute. Special enchantments mostly have defined effects that can't have a negative modifier, they will sometimes use the Drain button nonetheless. When enchanting for fetishes you'll only have 4 options. They are, respectively: Remove fetish, Decrease Interest, Increase Interest and Give Fetish. Choose accordingly.
4. Add Button: After choosing the exact enchantment you want your item to have, click this button. It also displays the cost in essences that will be added to the final price. This step is also reversable, and you can do so on the following area.
5. Enchantment List: All the enchantments currently in the item and to be added will be displayed here, like a shopping cart, with the total cost, limit and name (which you can change) displayed above. Clothes and weapons can be enchanted multiple times, allowing you to remove enchantments already in them, though doing so costs essences. Potions can only be enchanted once, so you should be careful during early game on higher difficulties, when getting items and essences is troublesome. Enchantments added during the current enchanting session that have not yet been confirmed can be removed for free. The essence cost for removing enchantments will be displayed over the X symbol if it applies.
6. Final Product: Hovering your mouse over this icon will display the end result. Check if the item is what you want if you're still unsure and move on.
7. Save/Load Presets: Optional. This button will bring you to a screen similar to the Savegame screen, allowing you to save the potion you are preparing or loading potions saved before. There are no presets but if you use certain potions frequently you should consider making some.
8. Craft Button: Clicking this will confirm the changes made and, if you have only one item of the kind you chose to enchant, will close the enchating window. The button will be greyed out if you don't have enough essences and leaving without clicking it will undo all this process(except saving and deleting potion recipes).
This should cover everything about enchanting that isn't explained in the game. The rest (what is enchanting, what are Essences, how to get them, their lore and their uses) is explained early on.
This is extremely simple stuff, mind you, and anyone with half a brain should be able to comprehend how it works by reading the tooltips and exploring the hud a bit only, but alas, be spoonfed.