what all would cause the gears not to shift right

What is your question?

All of a sudden my car is having trouble with gears. I have to put it in neutral first before it will move in reverse, and it jerks forward in drive and dies out and sometimes stops. I changed all fluids. I may be missing bar that keeps transmission in place. Could this be a part of problem. I am a 68 yr. Old disabled female that needs her car badly