If it really is a yam and not a sweet potato - I found this for you on the internet:
isu (yam - boiled plain)
Depending on the size of the yams you are able to buy, and what you are eating it with, each tuber should feed about 4-6 people.
Yams
Water
Salt
Slice the yams into pieces that are about 1 inch (2.5 centimeters) in width.
Peel the skins off the yams.
Rinse the yams.
Place the yams in a pot and add enough water to cover it.
Add about 2 teaspoons of salt.
Cook the yams for about 30 minutes, checking every 10 minutes or so to see if the yams are soft enough (a fork should be able to go through with ease).
Drain the yams.
Serve with stew, or eggs, or beans, etc. etc.
fried yam
Non-detailed instructions:
Cut the yam up into small strips.
Put vegetable oil into a pot, until it is at least 2 inches (or about 5 centimeters) high...it should cover the strips completely while cooking. Place on low heat, and allow it to heat up.
Once the oil is hot, place some of the strips into the oil. Allow it to cook and fry the strip, making sure that it cooks to the inside.
Yams usually don't soak up much oil, but if you want, you can place them directly on napkins to soak up some of the extra oil.