(HTML) How can I send a message through gmail that automatically generates the text I type in textboxes of my site?

So I am making an HTML website and I am trying to make a button that sends a message through Gmail. In fact, I have already done this; I made a button that sends a link to a preset message for the user to send to me. The problem is that I want to make the body of the message information that I have typed into text boxes of my Html website. In other words, I want the message that I send to basically automatically have the things I've typed in the textboxes of my website. (See the posted code below to better understand what I'm saying)

The textboxes I'm talking about:

AND I want the information that I type into the textboxes to automatically appear in the body of the message in Gmail after clicking this link/send button.

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