Basically it's all complicated chemistry stuff.
17b-estradiol is the chemical compound that will function as an agonist of estrogen receptors in your body causing feminizing effects.
17b estradiol acetate, like estradiol valerate, are the 17b-estradiol compound bound to an ester (acetate or valerate respectively) to form a new compound. The new compounds in the context of this thread act as prodrugs (drugs that metabolize into their parent compound estradiol17b). As such they are virtually equivalent to each other.
This is in contrast to compounds that are truly different chemicals and not prodrugs, like ethinylestradiol, which is the estradiol compound with an ethinyl group substituted into its structure. It won't be metabolized into estradiol but is still an estrogen agonist in its own right.
As for WHY there's so many different compounds. In the case of ethinylestradiol it changes how the original compound (estradiol) is metabolized, resulting in a much more potent chemical by mass for its biological effects. In the case of estradiol valerate, it increases its solubility in oil making it more suitable for injections and other uses. In the case of estradiol acetate, it's likely to change its properties in such a way as to make it more suited to its route of administration (like as a gel, vaginal ring, etc).
Sorry I don't know more about exactly how the acetate ester affects the compound, I'm very unfamiliar with that derivative of estradiol.
Short version: There's effectively no difference, estradiol acetate is listed as a prodrug of 17b estradiol, so it's pretty much substitutable.
Disclaimer: I am not a doctor and I don't have a degree in chemistry, so my information may be mistaken.
