The big three, the trifecta of smartphones, communications-wise are phone calls, texting, and e-mailing. As in the two just covered, the apps that come with your phone or tablet will do the basics of these better than an App Inventor app.
But, of course, we have the flexibility, as we did above, to add our own magic touch, and we'll do that here.
First, here's how simple it is to send e-mail from an App Inventor app. In Design, you need a button and drop the ActivityStarter in as a non-visual component. In the Properties column for it, type the same information as we use to call a web page, android.action.intent.VIEW. Leave everything else blank.
In Blocks Editor, use the button click frame block for whichever button you want to use for sending the e-mail. With only one in my example, that would be Button1.Click, but it could be Button26.Click or, if you renamed them as you should with that many buttons, perhaps Send_Email.Click.
Fill your button as shown in...