You can create a PlayOsmo account on PlayOsmo.com.
With a PlayOsmo account, you can keep track of your Osmo Credits, order history (including printable receipts and referral links for all of your orders), and payment methods, as well as add items to your wishlist.
Note that these accounts are different from myOsmo accounts (where you can save your game progress and request replacement pieces, among other things).