What method are you using to select the person from the main image? There are many people on the forum much better/experienced at this than I am, but I generally use the Lasso Tool. Once you’ve used it to select the person, you should have your selection totally encircled by those (in)famous marching ants, you can then either copy/paste or drag it into a new image.
Since the Lasso is rather hard to control, I normally make my selection and then drag it onto a new blank canvas, with a transparent background. From I use the eraser to get the rough spots removed. Then, once it’s all trimmed up, I move it to the background I’ve chosen.
The hardest thing for me to remember about using the Lasso: If, as you’re selecting, you need to shift the image in a window or just move the mouse around on the pad, you can "suspend" the action of the tool by holding down the space bar. If you let up on the mouse without doing that, you’ll wind up with a really weird shape!
I just did a quick selection and verified that the instructions I gave work. (I began to have this horrible feeling I’d steered you wrong.)
If you still can’t get this to work, repost and give us a step by step of what you’re doing and the point at which you’re running into trouble. With luck, you’ll get someone to respond who’s much better at this than me! 🙂
