To send a message from a record, firstly ensure you or your System Administrator have completed the steps in the article "Page layout configuration".
Once the previously mentioned steps have been completed you should be able to see the "Send Message" component on the relevant pages as shown on the Lead page in the screenshot below. To send an SMS, simply ensure the number field is populated with the correct mobile number, then enter the message body you would like to send in the Message field. When you are ready press "Send". On successful send a toast notification will display and the message will be recorded as a Message record (note the related list may require you to refresh the page to update).
Congratulations, you have just sent an SMS message from a Salesforce record page. You can automate the sending of messages by using our invocable actions to send SMS messages in Flow, or send messages in Apex through our Apex API.