The Engineer is the sixth class in the line of playable classes in Team Fortress 2. He shares the Defense catergory with the Demoman and Heavy. He has the ability to make turrets to defend a certain spot, a dispenser to heal, give ammo to player's, give metal to other engineers, and transporter's that teleport your teammates to an exit teleporter.
StrategeyPlaying the engineer you can aid your teammates in many ways. If you play him defensively you should put turrets near an enterance or a defense point.