My wife went through the same thing. I ride with her about 3 to 5 times per week. She has a MTB - based hybrid bike. I would ride behind her and tell her to move the left up a gear or the right down a gear. It took her about 4 rides to get the hang of it and now she shifts often and properly. Perhaps you can get someone in the neighborhood to ride with you and provide that sort of input.

One thing I would advise to start is to stay in the middle chainring in the beginning all the time (assuming you have a triple.) I'm talking about the gears right by the pedals. Then you will only have 9 or 10 or however many gears to worry about. Those are the ones on the rear wheel that you control with your right hand. After you get that under control you can then add the other two chainrings to the mix and be shifting with the best of them. Welcome to the wonderful world of cycling.