Another tofu lesson!
There are several different types of tofu - silken, firm, extra-firm and sprouted. While they are similar and can often be interchanged in recipes, there are a few differences. Tofu, in general, is very high in protein and low in calories. It's also quite versatile and on its own, pretty tasteless, so it lends well to many flavors. For more on what tofu is, rather than the difference in types, check out Scott's tofu post.
Silken tofu is just how it sounds, silky. It is great for making sauces and creams because of it's smooth and pudding-like texture. You can even eat it by itself with a spoon as a dessert sauce. Silken tofu is also great for making Pumpkin Pie (p. 218, HHC) or Creamy Dijon Pasta (p. 197, EHH). You can find silken tofu in the refrigerated section of the store or in a Tetra Pack on shelf in an aisle (Mori-Nu is the most common shelf-stable brand). While some may consider the shelf-stable version a little silkier or smoother, you generally can use either in a recipe that calls for silken tofu. The Tetra Pak version is great for taking on trips too, since it is shelf stable and doesn't need to be refrigerated until opened.
With Mori-Nu and silken tofus in general, there is not much difference between them levels of firmness is marginal, so don't worry too much about what kind you have. Silken is silken.
However there IS a difference between firm and extra-firm tofu with the refrigerated kind. Extra-firm is much firmer than Firm. Firm and Extra-Firm tofu works best for when the tofu needs to hold together, such as in stir-fries or when you're making Baked Tofu (pg. 138, HHC), or crumbled as in HH's Tofu Scramble. Note that if the recipe calls for cubing the tofu into small pieces, the firmer the better.
I once used firm tofu once in place of silken tofu when making HH's Sour Cream (p. 274, EHH). I ran the firm tofu through the blender a few times by itself with a little nondairy milk before making the recipe so it was somewhat silken in texture. It wasn't quite as creamy as usual, but it still worked in a pinch.
On the flip side, you generally can't substitute the silken for firm or extra-firm.
Sprouted tofu, meanwhile, is the same as regular tofu, except it is made from sprouted soy beans. While there is no difference in how you would cook with sprouted tofu (it is still labelled as firm, extra-firm, etc) there is a difference nutritionally. Sprouted tofu generally has more calories and fat than regular tofu, but also more protein.
Lastly, if you don't like the texture of tofu, you can try freezing it. Freezing makes it a little more chewier. The color also changes when frozen, but will go back to it's off-white shade once thawed.