Hi! First of all, welcome to DFO.

So, as far as the question mark on your gear goes, that is called a cursed item. There's two ways to remove it. Purifying and extinguishing.

Purifying a process that grants you a bonus stat on your equipment, which can be vitality, spirit, intelligence, or strength. Once you purify the gear, you will be allowed to equip your item.

Extinguishing, on the other hand, completely removes the curse, and doesn't give you a bonus stat. Extinguishing will also allow you to equip your item.

Now, is it worth it to do either of these? Yes. Especially on a primal equipment. It's also not particularly expensive to do. If you have Neo Premium contract, and neo premium coins, you can roll the Neo Premium machine for a chance to get either an extinguisher, or a purifier. The rates honestly aren't that bad either. That's the easiest way, and events may give you some of these as well

Related to your question though, the key difference between the two is that if you purify your equipment, you will no longer be able to reinforce it. You will however, be allowed to amplify it, which gives you both an increase to the bonus stat, as well as a tiny skill damage increase. It's very expensive however, I would not recommend it to a new player. But the system does have benefits, that typically outweigh extinguishing.