Workers are used to process build and deployment jobs.
Global workers are available for building at rocketgit.com, so
just configure a build webhook.
Cost - it is used to decide on which worker to send a job; bigger = less
chances to choose it.
Key - it is used to authenticate the connection from worker.
To learn how to configure a build machine, go
here.
The worker will connect automatically and will be ready to receive build jobs.