I assume you are talking about fresh fennel bulb. It has a strong licorice flavor, but gets much much milder and sweetens upon cooking. Below is a basic recipe:
Cut fennel bulb in half, slice each half into four slices
Sauté onions in a pan for a couple of minutes.
Add fennel and cover, cooking over a medium heat.
Cook for 10-12 minutes or until soft, stirring occasionally.
When you stir the fennel and onions keep the lid held over the pan so the
condensation drips in and the fennel stays moist.
Remove the lid and turn the heat to medium-high, cook until the fennel is
brownish, about another 5 minutes.
Add salt and pepper and any other spices of your choice.
Taken from:
http://vermontvalleyfarm.wordpress.com/recipes/fennel/
Some more ideas:
http://www.twoonionfarm.com/Newsletters/RecipeSearch.htm#...
Fennel Sauce:
2-3 fennel bulbs
1 Tblsp each olive oil and butter
Salt
Juice and grated zest of 1 lemon; or 2 Tblsp
lemon juice and a dash of dry lemon zest
1 clove garlic, crushed
Black pepper
Wash the fennel, quarter and slice it thinly
(you don't have to cut the core out in this
recipe, because it will soften through the
cooking process). Melt the olive oil and butter
in a skillet. Add the fennel and sauté over
medium-high heat, stirring occasionally, until
fennel is beginning to brown. Add salt, lemon
juice, and 1 cup water. Reduce heat, and cook,
partly covered, until fennel is very soft and
deep gold color. During cooking, you can add
extra water as needed if water evaporates
before fennel is soft; but try to have all liquid
evaporated when fennel is done cooking. Add
garlic, lemon zest, and black pepper. Serve
over pasta topped with cheese.