Workflow rules are automated process which act on certain criteria, It eliminates development effort by providing option in point and click. We can complete different business logic using Workflow rules in Salesforce.

A workflow creation is 3 steps process and we can clearly understand it using following diagram

1. Where to Perform  :

This is first step where we select the Object on which we are going to perform any action. It can be any standard object such as Account, Contact, Opportunity, Task etc. or any custom object.

2. When to Perform :

This is second step where we select when we are going to perform this action. For example :

1. Perform a action if Account name updated.

2. Perform a action when Case priority is high.

3. Perform an action if Opportunity Stage is Won.

3. What to Perform : 

This is last step where we select what action we are going to perform. Salesforce support 4 types of Action

1. Create a new Task : Create a new task for object selected in Step 1

2. Send a email alert : Sent email alert if criteria match. for example if you want to notify your Opportunity owner if Opportunity stage is won you will select this action.

3. Update a field : Update any existing field with value

4. Send Outbound message : Send a secure configurable API message (in XML format) to a designated listener. For example, automatically initiate the reimbursement process for an approved expense report by triggering an outbound API message to an external HR system..

Here is a complete sample workflow after following all above steps.

Once you are done by creating a workflow last step include to activate this workflow. If you will not activate Workflow it will not run.

Note: In Dreamforce 14 Salesforce unveiled Lightning Process builder which is more powerful than workflow in Salesforce. For this tutorial we are limiting ourself with workflow only. I will cover Lighting Process builder in Salesforce Intermediate Tutorials section. you can read more about Workflow in Salesforce here.