GPS Position Hold enhances the auto-level mode to also keep the copter in the same position. It will bank the copter in order to counteract any external force such as wind. Now when you enable this feature the copter stays in one spot!
GPS Return to Home (RTH) when enabled will take full control of the copter, turning it toward the home position and then flying on it's own back to the set home position. The home position is set each time the copter motors are armed. Lost orientation of the copter? Lost sight of it? Turn on the GPS RTH and it will come right back to you. Hopefully, there are no trees or low flying planes in the way! It isnt that smart.
Bluetooth Remote Easily add a Bluetooth or 3DR radio and control features and parameters of your copter while in flight! Get fancy heads-up displays with telemetry, power output, GPS+GoogleMap and more. Also control flight parameters while in the air including Position & RTH control parameters. I recommend an Android tablet or phone but you can also use your laptop. If you plan on using a laptop then use the 3DR radios, they are easier to use and work better. Otherwise, with Android we are left with only bluetooth as a choice since they dont support external radio links.
Compass Hold (MAG hold) when enabled will keep the copter pointing in the same compass direction. You can still YAW, changing the copter's heading, and the copter will then maintain the new heading. This is great for beginner flyers, they can concentrate on the throttle, roll and pitch without worrying about maintaining the copter's heading. The ACC mode, or auto-level, has been renamed to ANGLE mode and the behavior hasn't changed.
Head free (Care free) mode uses the compass and your last known position to transform the commanded stick input from your transmitter from the persepective of the copter into the persepective of you the pilot. For most beginner pilots the toughest part of flying is projecting yourself onto the copters orientation so that you can determine how you need to move the control stick. You have to imagine in your minds eye, you are sitting on the copter and facing the same direction. Head free mode removes this burden! The copter control software, knowing where you are, adjusts the stick input so that roll left is always left on the copter from your perspective and roll right is always right, and the same with the pitch. You take away the notion of a "front" on the copter, there is no front anymore!
Flip training HORIZON mode is a combination of the ACC/ANGLE mode and regular acrobat mode (no auto-level). When you are not touching the roll/pitch stick then the copter auto-levels, but when you start putting in bank or pitch angles then the copter morphs to acrobat mode. This mode is basically a flip-trainer. It allows you to full bank or pitch to begin a flip and then let go of the stick to have the copter right itself. It really works, and is an awesome feature, but you can still crash the copter if you attempt it at low altitude. Altitude is your friend here!