So essentially if you sell an item it is no longer there to be 'used', you'll notice each item has an offence / defence rating so you want to select the item of clothing which has the highest rating to make your character as strong as possible.
That covers the 'attributes' of an item
In terms of how your character looks, when you are on the main page for the gear, hover over the area (cloak for example) and press X on Xbox, square on PS5 no idea on PC and you can customise the look of an item.
Any item you have found can be used for the look weather you have sold it or not, this way you can make you character look how you want, whilst freeing up gear slots, and ensuring you always have the strongest clothing on.
I'll try to get some photos of what I mean later on unless this now makes sense or unless someone can interpret my gibberish and translate it to a sensical response