I want to make a discount for only ONE category in Catalog Price Rules but I dont understand the Conditions tab.
In Catalog Price Rules condition, selectect category to only apply discount.
As per your screen shot, 2,3,62,64 category to apply discoont. All other categories excude from apply discount.
If you want to apply discount on paticluar category, select it in this condition. all other category which are not selecte in condition, it will exclude from discount.
Let me know if you have any questions from above.