First you have to set up your Email Server: you can review these steps in the ProcessMaker documentation: https://wiki.processmaker.com/3.3/Email_Settings
I attached images with my configuration using the link I mentioned at the top, after that I created a new BPMN project called (Send a Email) in which it consists of a single task called (Send email test), and i created a dynaform consisting of 2 text fields: name and email.
After I created a trigger in which the PMFSendMessage function was used to send the mail. The trigger is assigned to the task after the dynaform.
I Attached images about what I did.
You can check for more information about the PMPSendMessage function in the ProcessMaker documentation: https://wiki.processmaker.com/3.2/ProcessMaker_Functions/Email_Functions#PMFSendMessage.28.29
Likewise, one of the important parameters that the PMPSendMessage function needs is a template. You can create your template by checking the documentation of the processmaker: https://wiki.processmaker.com/3.2/Templates