Tanks can change the flow of a match in Battlefield 6 REDSEC. They give firepower and protection. They also make you a big target. This guide explains how to get a tank and how to use one without getting destroyed.
How to get tanks
There are two main ways to get a tank in REDSEC. The first way is to complete missions that award a golden vehicle keycard. These missions look like regular objectives in the mission wheel. If one of your missions lists a golden vehicle keycard as a reward, then finish that mission and claim the card. The game will show you a nearby vehicle trailer. Go to the trailer and insert the keycard. Wait through the opening animation and then drive the tank out.

If none of your missions offer a golden keycard, then tanks may not be available nearby. Let your mission list cycle a few times. New missions can appear that include the keycard reward. If you see a vehicle trailer on the map, then be patient and watch for a mission that pays out a tank keycard.
The second way is to take one from another squad with a Tank Hunter mission. Those missions ask you to find an active enemy tank and either destroy it or steal it. Stealing a tank is risky. You will need to damage it enough that the crew leaves or jumps out. One of your teammates must then get in and survive long enough for an Engineer to repair the vehicle. More often, teams simply destroy the tank and take cover when the wreck collapses.
Tactics and cautions
Take an Engineer along with you when you intend to take a tank. Vehicles are repaired by engineers and armor refilled. A tank that is not repaired will die shortly. Keep an eye on the sky. Airplanes and guided missiles have short work with ground armor. Cover and do not take long open runs. Trek between structures as much as possible. Have your squad near you to be able to clear the infantry and fix where necessary.

The tank is to be an implement, not an instrument; Go out to survey in case the place is overheated. Change drivers so that the tank is not standing there burning. Should you be in need of retreat, you must go into positions of friendliness and smoke screens. Ensure your team has anti-vehicle tools that will be used in the event of a close battle, and also have provisions to replenish the tank.
Tanks are rewards of good teamwork and planning. They also draw the attention of the whole map. When you have one, then make it like a mission goal and continue to make your squad operate as a team.