An API is a set of programming code that enables data transmission between one software product and another.
It is standardized technology that allows different applications to "talk" to each other. These can include the use of data warehouses like a SQl server, accessing an Oracle or Microsoft Access database, among others.
Integrating into these systems can require a sophisticated, custom approach. As systems get more sophisticated and are modified, it is not your concern because the API and its benefits will continue to work.
The Bridge works on the basis of "Signals". A Signal is generally a sign (not choice) to Buy or Sell with explicit conditions. The Bridge forms 4 sorts of Signals: