My 2004 BMW 745 has been sitting in my carport after I had an in home accident,The battery is dead.I got an electrical charger but do not know how to re charge.Some say undr the hood.Others say trhrough the trunk,Please give me a step by step way of doing it right.Thanks in advance; RMG

The jumper cable connection point under the hood is directly connected to the battery. If you are not familiar with charging batteries, it is much better that you connect your charger under the hood.
Leave the ignition turned off. Connect the positive (red) clamp to the jumper cable connector under the hood. Connect the negative (black) clamp to a bare metal ground point such as a bolt or lifting lug on the engine. Then plug in and turn on the charger. Let it charge for several hours before trying to start the car.
If this is the original battery, it likely won't ever really work well again. Maintenance free batteries do not respond well to being completely discharged, and at 7+ years of age, it is due for replacement anyway. I had to replace the battery in my wife's 2004 BMW 330 about four months ago, and it had never been allowed to go dead,