User can create new message templates before sending the actual message under various tabs.
To add Template under Lead:
Click Leads tab & click the desired Lead record from where SMS is to be sent.
Click Send SMS button & click Create Template.
Enter valid data in all fields as shown.
Click Save button.
The message template is now ready to be used.
Check below screenshots for the same.
Success message will be displayed once done.
Now the page will show the values populated as saved while creating the template.
User can type the message if required and then click Send button.
Success message will be displayed on done.
Note: Here user has a facility to send the template via SMS Now or Later some date/time using the related drop down value. This is explained in detail on other help link.
Note that by clicking the blue plus button, the Api Name as selected will appear in the message body and this will be converted to the actual while Send SMS.
In the same way, the SMS Template can be added under Contact & Opportunity objects as well.