Re: I need some help... (Sims 4 Farmers Market)

As @PugLove888 said, you need the "Get to Work" expansion pack to buy/build & run a retail store, (which is 50%off at the moment https://www.ea.com/en-gb/games/the-sims/the-sims-4/pc/store). I love that expansion pack. Lots of good info about how it works at this link: http://www.carls-sims-4-guide.com/expansionpacks/gettowork/retail/ )

Alternatively (but less fun/satisfying) you should be able to sell them directly in inventory in the buy/build mode. Grab the item and drag it to the greyed area to the left of the inventory that has a simoleon (coin) icon. Some items they make will be found in their personal inventory, and some may be in the household inventory (furniture). 

If you have 'City Living' you can use a 'Come and Get It' table to sell items, but I find that to be a pain. I would definitely recommend buying "Get to Work" then selling your goods at a store more than the 'City Living' table route.

Hope that helps.