Here is a Process Automation Cheat Sheet to help you determine which automation tool to use in Salesforce, given your specific scenario.
Resources:
Process Automation Cheat Sheet (PDF) -
https://resources.docs.salesforce.com/rel1/doc/en-us/static/pdf/SF_Process_Automation_cheatsheet_web.pdf
Which Automation Tool Do I Use?
https://help.salesforce.com/articleView?id=process_which_tool.htm&type=5
In this lesson we discuss the four actions available from Workflow Rules - Tasks, Email Alerts, Field Updates and Outbound Messages.
In this lesson we add a field update to a workflow rule. Good times are had by all. It's that simple.
Fun fact - you can indeed perform (some) cross-object field updates via Workflow Rules. In this lesson we discuss the details and limitations of doing just that.
