If you have your inventory window open, there should be a "Simoleon Symbol", on the left side of the window. It looks like a coin. Anything that can be sold, you can drag to that window. It will show the price. Drop it there & it will sell the item. Not everything can be sold. It will tell you. Not everything gives you money. Reward potions don't give you any money. It's better to drop those in the recycle bin, for 10 sim. Water glasses might be better to sell, too. For things like chairs & furniture, they won't be in your personal inventory. You have to go to build mode. On the far left bottom corner, there will be a picture of an open box. This is where you will find furniture you've built.