Resource Blocks are units of compute capacity in Tableau Cloud. Resource Blocks run Tableau Prep Conductor flows. Each Resource Block can run one flow at a time so the number of flows you can run concurrently is equal to the number of Resource Blocks that you have.
When you license Data Management for Tableau Cloud, you must purchase at least one Resource Block. To purchase more Resource Blocks, contact your account manager (or go to the Tableau pricing(Link opens in a new window) page for more information).