Unlike shared hosting accounts, dedicated servers involves renting a full physical computer server for your own exclusive use. You will have full administrative control over the machine and can install anything on the machine as long as they are legal. Basically, it is not shared with anyone else.
Unmetered bandwidth is not unlimited bandwidth but it is set at a specific bandwidth pipe size usually 10mbps or 20mbps. Think of a server as a car and the unmetered bandwidth is like having unlimited supply of gas but you are still controlled by the maximum speed limit of the car.
The other method of offering dedicated servers is by providing a fixed amount of free bandwidth like 1000gb a month but you are free to burst to 10mbps or 100mbps. Generally, it is like a car which comes with a tank of gas and you can drive as fast or as far as you want but if you exhaust that tank of gas, you can top up but you pay for it.