The term API stands for ”Application Programming Interface”. An API can help you gather and connect different systems and data, and present these in one interface. That makes it easier to update data and find the information you need.
Your user account is you as individual; it's not your company. When signing up for Xena you get a personal profile in Xena. With this profile you can create one og more fiscal for free. This article explains how to invite other users into your fiscal.