Stevia is a 100% natural plant extract that is 200-300 times sweeter than sugar. It is the best alternative to sugar on the market and preliminary studies suggest it’s actually beneficial for diabetics. Use (a tiny amount of it) wherever you would normally use sugar (beverages, cooking, baking, etc.). The taste of Stevia depends on whether it is whole leaf stevia, or stevia extract; how pure the extract is and whether there are any fillers added to it. The brands I’ve selected are of the highest/purest quality, with no added fillers.
If you want the stevia taste to be completely undetectable in your baking, then use half regular sweetener (eg. honey, maple syrup, rapadura or turbinado sugar) and use stevia extract for the other half. A good rule of thumb is 1/2 tsp stevia extract = 1 cup sugar. So, for example, if your cake recipe calls for 1 cup of sugar, then use 1/2 cup sugar and 1/4 tsp stevia.
Also, this stevia extract jar lists a super light weight because it is so finely powdered, but there's actually a good amount of product here - about the size of a regular spice bottle (approx. 4" x 1.5")
NOTE: The difference in pricing of the stevia products is because some are WHOLE stevia leaf (which is less sweet and has a much stronger "licorice" aftertaste) and the more expensive ones are white, stevia EXTRACT (which has a very slight aftertaste and is the sweetest, hence you use a lot less - I prefer this extract).