店 shelters 占 (to occupy, also the sound) under 广, the lean-to roof radical for buildings. A spot occupied under a roof to sell things — a shop, unchanged in concept for two millennia.
店 marks every storefront in China: 饭店 (restaurant/hotel — 'rice shop', with 饭), 书店 (bookshop, with 书), 商店 (general store), 网店 (online shop — the roof went digital). The suffix 小店 ('my humble shop') is how owners modestly refer to their own business. Walk any Chinese street and count the 店 signs — it's the character you'll read most often outdoors.
Under a roof 广, a spot occupied 占 to sell — a SHOP.
网店 'net shop' — China's e-commerce giants run on the same 店 that named Tang-dynasty market stalls.