Once you have created yourself an account you will find some important API tokens (secret keys) in your Account in the Account Menu to the right of the top menu bar.
Once selected the Token Dialogue is shown where Tokens can be copied from:
Shop-Token The shop token allows loading of Templates and Snippets, upload images and saving / loading the current layout
Service-Token The secret service token has access to the production API and can render PDFs or PNGs. It will be shown only on Accounts with administrative access.
Embedd Here you find an easy embedding example code for the current document. See Below Ebedd as iframe.
The service token should only get used on server side to process orders. With it billable orders can be started. To protect your account never embedd the service token into a web-site!