To use the items you unlock when you level up you have to have the right appliance. If you're able to purchase an appliance (which is kinda difficult because you can only buy them at certain levels) you'll notice that there are 3 different this; a stove, an oven & a grill. You can only cook certain things on each appliance. Things like beef stew & lobster are for the stove, pizza & pumpkin pie go in the oven, & burgers
go on the grill. Hope this helps.