function sendSelectedEmails() {
var sheet = SpreadsheetApp.getActiveSheet();
var activeRange = sheet.getActiveRange();
var data = activeRange.getValues();
for (i in data) {
var row = data[i];
var emailAddress = row[0];
var subject = row[1];
var message = row[2];
MailApp.sendEmail(emailAddress, subject, message);
}
}