You pick your Attributes (ST, IQ, HT, DX) as normal. To be an animal or the ability to transform to one or more animal types is an advantage.
So you must first pick an animal type, then you get an amount of starting Bio-E specified in the animal description section for the animals you selected. You can increase the Bio-E by making the animal bigger or smaller. The total Bio-E is the cost of points you have after increasing/decreasing starting Bio-E. With these Bio-E points you can upgrade your animal. The total cost in CP for all animal forms you selected is the sum of all Bio-E points plus the additional points for the transformation if any.