Here's one that should be a little simpler than it is. In a basic e-mail in the most recent version of the gmail app, the options to reply all and forward e-mails are somewhat hidden. You've got top-level access to star an e-mail (which we find ourselves accidentally hitting far too often) or to replay to the original sender.

To reply to everyone in the e-mail, or to forward the e-mail, you'll need to first hit the little triangle button that we've highlighted above. Then you'll have options to reply all or forward.