The concept of "gates" is introduced to help you understand how to deal with vehicles around you.
Imagine four gates surround your vehicle at all times. One gate is located in front of the vehicle, one is behind and one is on each side of the vehicle.
When you are travelling alone in the centre lane of a road where there are three lanes provided in the direction that you are travelling, all four gates are open to you. This means you can move ahead, slow down and drop back, or move to your right or left, and still continue uninterrupted movement.
If a gate is open you can drive into it whenever you want to. A safe driver always tries to have at least two open gates to provide options for emergency movement.
If a gate is closed - by another vehicle, a curb, a guardrail or even deep snow - you lose the opportunity to move into the area that gate controls.
Check your mirrors to ensure you know which gates are open. You need to check your inside mirror and your left outside mirror often. When you are a more experienced driver, start using your right mirror, if you have one.
While you are not required to identify a vehicle in detail, you should know whether the rear gate is open so that you could drop back if you wished. If the vehicle behind you is tailgating, then your rear gate is closed.
You need to leave extra following distance ahead to allow room if you have to stop. Increase your following distance to five or six seconds. (See Using time to estimate your following distance.)
How often you check your mirrors depends upon the number of lanes and the amount of traffic. If you have ever been surprised by a vehicle overtaking you, then you are not looking in your mirrors often enough.