Wheat is a crop, that you can harvest and not eat directly. You have to use it in a Refinery to get Flour out of it. With this Flour you can bake a Bread in the Fireplace.
It takes about 90 minutes (one and a half hours) for the crop to be ready to harvest. The crop has 3 growth stages after sown, it takes 20 minutes to reach stage 1, another 25 minutes to ready stage 2 and another 45 whole minutes to be ready to harvest.
You can buy the seed for wheat from Steph.
Step 1 - put your Wheat in the Refinery, add some Fuel and convert it into Flour:
Step 2 - put the Flour in your Fireplace, this way you get Bread out of it:
If you add Banana to the recipe, you get Banana Bread.