My grocery carries fresh cassava (a.k.a. yuca) but I think it's a pain to process, or at least it seems that way from what I've seen on Chopped. So, I prefer to buy the frozen kind. The only thing to watch out for is pulling out the tough weird root-like stem thing running through the center; frozen yuca has been peeled but that stem hasn't been removed.
If you're going with fresh, make sure you buy one where the flesh is completely and beautifully white. It might be difficult to inspect but at my store, they already have the yuca chopped in half to expose the flesh which makes for easy inspection. There are plenty of authentic, useful resources out there that will help you navigate how to prep cassava so I'm not going to even attempt to make a guide when in all honesty, I've only ever dealt with frozen yuca. But it doesn't even matter because the frozen tastes just as delicious as fresh.
1½ lbs. frozen yuca
oil for frying
+ salt to taste
1 clove garlic, finely minced
1 tablespoon lime juice
3 tablespoons sour orange juice
¼ teaspoon salt
¼ teaspoon pepper
2 tablespoons olive oil
One v. important note is that you should never eat raw yuca. Yuca contains cyanide and is toxic in its raw form. There are several varieties of cassava, some of which are more toxic than others. Sweet cassava is typically what is available in groceries in the States (due to our proximity to Latin America) and this variety is the least toxic and is made safe to eat simply by boiling. Bitter varieties of cassava require days of soaking before cooking, but bitter varieties are typically found in Africa.
Start by boiling the frozen yuca until tender; use a sharp knife to pierce the yuca to test its doneness, similar to testing potatoes.