There are a few options when selling used clothes:
Apps: There are several big apps with marketplaces where you can sell used clothes, shoes and accessories. Remember to be realistic about the price and try to take good photos to increase the chance of selling your wardrobe.
Social media: A lot of people sell clothes (and everything else) in groups or pages on different social media platforms. Facebook Marketplace or groups are probably the most common channels for getting in touch with people that want to shop.
Second hand shops: Some second hand shops buy clothes directly from you. Some allow you to display your items in their shop and give you money once sold. These shops are normally a bit more picky about what they buy, so it is mostly suitable for vintage, designer or unique pieces that fit their aesthetic.