Workflow Basics explains what workflow is, lists many (but not all) of the tasks it can automate, what makes workflow make, and when the workflow applies to orders.
Automation rules are powerful tools that will save you a ton of time. Use them with care, as they can automatically change shipping preferences and debit your postage and shipping accounts. Always test rules on a small group of orders (for example two to four orders) before applying broadly. Know and understand the shipping services in detail. Read all relevant documentation before auto-shipping orders.