Configure your website Credits System from the Admin Panel > Social Networking > Credits page.

Here you can customize the Language & Phrases, such as want you want to call your website's currency, and the configurations, such as whether or not to have another account to, i.e. for a Savings & Loan account.  Also, choose how many credits each member starts out with, and configure a Credits Purchase Form/Button.

To embed your Credits Purchase form/button, just copy/paste the Placeholder Text from this page, to the Add/Edit page where you want it.