"Last, but not least, is the Engineer Training. Go to the Training menus and select him to Start.
"The Engineer's class ability is to make useful buildings, like the Teleporter you used previously, and the Sentries you've seen a few times now. The pop ups will explain how to build things, and ask you to make a Dispenser in front of you and upgrade it to level 3. Hitting it with your Wrench will make it build faster, and once it has been built, hitting it will upgrade it at the expense of some metal.
"Keep following the pop-ups, as they explain how to make a Sentry. Upgrade it to Level 3, getting metal from your Dispenser or the Ammo crate. After you are done, some Red bots will attack so stand behind your sentry so you'll be safe. Both your Sentry and Dispenser got damaged in the attack, so repair them by hitting them with your wrench (this also costs metal).
"Now you learn that you can move buildings by right clicking them, and how to build Teleporters. You can also rotate a building you can carrying (or one you are about to build) by right clicking.
"After you've moved the Dispenser and built both Teleporters, you will be shown how to blow everything up. So pull out your Demolish tool and destroy all four of your buildings to finish.