User needs to have the Process Builder setup done for Contacts & Leads records in order to fire the adequate values and run through the validations.
For Contacts setup:
On top right of the page, look for the gear icon & click.
Click Setup.
Search for Process Builder in the search bar.
Select Contacts tab.
Click Contact on the flowchart.
Set the desired rule on right side of the page.
Click Save.
Now, click Send SMS displayed in blue square.
Set the desired rule on right side of the page, multiple rules can be set here.
Click Save.
The click Create History under Immediate Actions.
Set the desired rules here including the merge field under Value column.
Click Save.
Now, the rules are set for Contacts tab which will be fired as & when the condition is met and appropriate values will be set.
For Leads setup:
Follow the same steps for Leads as followed for Contacts tab above. Select Leads in fourth step above instead of Contacts.