Equipment are durable items that you permanently add to a tank unless you decide to sell them. You can only have three items of equipment on a tank so you need to choose what you want on it wisely. Equipment you purchase can be sold back and you will recoup a fraction of the cost, which may only be 50%. If you decide to sell your tank the depreciated price of equipment is taken into account. This means you should just buy equipment for tanks you want to keep and don't sell equipment to make room for another item. When purchasing equipment buy items that work in synergy, for example if you get the camouflage net, binocular telescopes and tank gun rammer you will be an excellent sniper.