Many connectors on Blockspring require you to signup for an API before they can be used.
For example, this block lets you search for tweets. Before you can run the block, you will need to connect Twitter to Blockspring. When you click a block that requires a connection, but you do not already have one, the steps will be given on the page.
Some API providers allow free usage of their API while others require payment. If an API is not free, you will likely need to provide payment info when creating an account on the API provider's website.
Blockspring does not charge you for running any API. If an API requires payment, and you do not have an active account with that API provider, running a block with the API will return an error.
If you are part of an organization, and also have access to view your organization's connections, you can see the connections on these two pages:
Organization APIs that use OAuth
Organization APIs that use secrets