// add label MyLabel to the first thread in the inbox
var label = GmailApp.getUserLabelByName("MyLabel");
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.addLabel(label);

// log the subject of the first message in the first thread in the inbox
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log(firstThread.getFirstMessageSubject());

// log the subject of the first message in the first thread in the inbox
var firstThread = GmailApp.getInboxThreads(0,1)[0];
var id = firstThread.getId();
// get same thread by it's id
var thread = GmailApp.getThreadById(id);
Logger.log(thread.getFirstMessageSubject() == firstThread.getFirstMessageSubject()); // will always log true

// log the names of the labels attached to the first thread in the inbox
var firstThread = GmailApp.getInboxThreads(0,1)[0];
var labels = firstThread.getLabels();
for (var i = 0; i < labels.length; i++) {
  Logger.log(labels[i].getName());
}

// log the date of the most recent message on the first thread in the inbox
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log(firstThread.getLastMessageDate());

// log the number of messages in the thread
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log(firstThread.getMessageCount());

// log the subjects of the messages in the thread
var firstThread = GmailApp.getInboxThreads(0,1)[0];
var messages = firstThread.getMessages();
for (var i = 0; i < messages.length; i++) {
  Logger.log(messages[i].getSubject());
}

// log if this thread has starred messages
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log('has starred : ' + firstThread.hasStarredMessages());

// log if this thread is marked important
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log('Important? : ' + firstThread.isImportant());

// log if this thread is a chat
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log('is in chats? : ' + firstThread.isInChats());

// log if this thread is in the inbox
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log('is in the inbox? : ' + firstThread.isInInbox());

// log if this thread is in the spam folder
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log('Spam? ' + firstThread.isInSpam());

// log if this thread is in the trash
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log('Trashed? ' + firstThread.isInTrash());

// log if this thread is unread
var firstThread = GmailApp.getInboxThreads(0,1)[0];
Logger.log('Unread? ' + firstThread.isUnread());

// mark first inbox thread as important
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.markImportant();

// mark first inbox thread as read
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.markRead();

// mark first inbox thread as unimportant
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.markUnimportant();

// mark first inbox thread as unread
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.markUnread();

// archive first inbox thread
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.moveToArchive();

// move first non-inbox thread to inbox
var firstThread = GmailApp.search("-in:inbox")[0];
firstThread.moveToInbox();

// move first inbox thread to spam
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.moveToSpam();

// move first inbox thread to trash
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.moveToTrash();

var firstThread = GmailApp.getInboxThreads(0,1)[0];
// ...do something that may take a while here....
firstThread.refresh(); // make sure it's up-to-date
// ...do more stuff with firstThread ...

function removeLabel(){
  var myLabel = GmailApp.getUserLabelByName('');
  var threads = myLabel.getThreads();
  for (var x in threads) {
   var thread = threads[x];
   thread.removeLabel(myLabel);
  }
}

// respond to author of last email in thread with acknowledgment
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.reply("Got your message");

// respond with html body text
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.reply("incapable of html", {
    htmlBody: "some html body text",
    noReply: true
  }
);

// respond to all with acknowledgment to first thread in the inbox
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.replyAll("Got your message");

// respond with html body text
var firstThread = GmailApp.getInboxThreads(0,1)[0];
firstThread.replyAll("incapable of html", {
    htmlBody: "some html body text",
    noReply: true
  }
);