There are many posts on this forum about stevia, and I suggest you do a search here and on the American herb forum, using the 'entire site' button.

Stevia cannot always be used as a substitute for sugar, except as a sweetener/flavour. For instance, it's not suitable for making jams or confectionery, because it doesn't form a 'toffee' or syrup. It can be used in jams which are intended for immediate use, as a flavouring, but you must use pectin to get the jam to set. Such jams will have a short shelf-life (about a week) because of the reduction of sugar, which acts as a preservative. You can add stevia to cakes, biscuits etc as a sweetener, but it does have a peculiar, earthy after-taste disliked by some.

The following advice should be regarded as a rough guide only. The sweetness of stevia can range anything from 10-600 times the sweetness of sugar, depending on where the stevia was grown, soil conditions, time of harvest, method of preparation, and many other factors.

Use dried, powdered leaves as a substitute for sugar. One tablespoon of stevia or less is equivalent to about 1 cup sugar. Some people notice a slight after-taste, while others do not. A liquid sweetener is made by pouring 1 litre boiling water over 1 tablespoon dried leaves and leaving to infuse. Refrigerate and use within a few days, or freeze for later. To make a syrup, place 4 teaspoons dried powdered leaves in a saucepan with 2 cups water, simmer slowly for 10-15 minutes. Cool and refrigerate. A teaspoon of Vitamin C powder may be added to act as a preservative. An infusion of fresh or dried leaves can be drunk as a beverage, hot or cold, or added to other herbs as a sweetener. If using fresh leaves to replace dried quantities listed above, multiply the amount 5 times. Approximately 6 large leaves chopped finely is a substitute for 1/2 cup of sugar for baking or in cooked recipes. 1 teaspoon of ground stevia is equal to 1 cup of sugar 2 drops of liquid essence is equal to 1 teaspoon sugar. A liquid sweetener can be made by steeping 1 tablespoon of dried stevia leaves in 1 litre of boiling water. An extract can be made by combining 1 cup vodka with 3/4 cup fresh stevia leaves in a jar. Shake every day for 2 weeks, then filter through a coffee filter. Add a drop to beverages.