Navigation theory for Private pilot
Magnetic Bearing: 
This is the direction of the plane's nose relative to magnetic north at the plane's current position. Simply stated, it's the bearing that your plane's heading indicator gives you. It's from 000 to 359 degrees(where 000 is north, 090 is east, 180 is south and so on). ATC directions are also given usually in magnetic bearings. Most aircraft heading indicators give reading in magnetic bearing only. Note that bearing is always stated in 3 digits. 

Magnetic heading/heading. Same as magnetic bearing. 

Track: 
This is where things get a bit complicated. Suppose your plane is flying with its nose pointed at 090 degrees(east). You also have a wind blowing in from 000(north). This 'blows' the plane to the south a bit. Now even though your plane is pointed towards east the direction of its flight path is different! This is where track comes in: it's the direction of the flight path of the plane. In some cases it may be the same as magnetic heading (no winds etc), in others it might be different (crosswinds).