im new to BMW. Where to add trans fluid to my 2007 BMW X5 4.8?

The drain and fill ports are on the side of the transmission. Check youtube on the procedure. You have to get the SUV up in the air on a level surface. So pick up 4 jack stands and a good jack. Some drain pans and fluid and a filter kit. You also have to have the transmission warmed when adding and a pump. Sometimes it's easier to have someone else service it. Good luck, with what you are describing, a fluid change probably won't help, almost sounds like rebuild time. Have a decent shop diagnose it.