OttoFMS is an application that runs on your FileMaker Server, and provides an automation engine, runtime features and a Developer API that you can use to automate your developer operations, and power up your FileMaker applications running on your FileMaker Server.
A good place to start your investigation of OttoFMS is to learn about its main concepts. They will provide you with an understanding of how OttoFMS works, and how you can use it to automate your FileMaker Server.
Check out the guides for how to use OttoFMS and its companion apps to achieve specific goals like data migration or using API Keys.
Below are some links to documentation that will help you get familiar with the general feature set, user interfaces and APIs that OttoFMS and its companions provide.