Those of you that updated to Android's new Gmail app have probably noticed that your little checkboxes have disappeared. So how do you select multiple messages? There are two simple ways.
One of Gmail's new features is the images on the left-hand side of your inbox. At a glance, you can see who sent the email without reading the name. If you have these contact images enabled, you can just tap on the images as if they were checkboxes, and that will select multiple messages.
However, if you want to turn sender images off, you can do so under Settings > General Settings. If you do so, selecting multiple messages is a bit different: just press and hold on a message in the inbox, and it will turn blue. After that, you can tap other messages to select them. This behaviour already exists in some other apps (like Messaging), so some of you may know about it already, but if not, there it is. Head on over to Android Police to read more and see a video of it in action.