To cut around your flower you can simply use the Magic Wand Tool, however, it may not always give you such a clean edge. This is where the Pen Tool comes in handy.
Simply make a path around the image you wish to keep, once you have done so, right-click on the image and choose "make selection", at this point a new dialog box will open prompting you to enter the "feather radius" which is how clean (or soft) you would like the edge of the image to be (the higher you set the number, the more blurry the image will become). It might be a good idea to leave this number at zero.
After you select your feather radius, you'll notice your image has the "marching ants" around it. At this point, you can simply drag the newly cut-out image over to a new layer using the Move Tool.
Of course, you'll want to have a layer open in the background if you choose to drag your image over onto it. To do this, go to File, New, and when the dialog box opens, set the desired height and width, so on and so forth and hit ok.
To simply select a whole layer to drag into another layer, press Ctrl A, bringing up yet again the marching ants. Then just drag that layer to your new layer using the Move Tool.
Well, I certainly hope I've helped with this. This is, of course how I do things, and if I'm doing something wrong here, I can always blame someone else.
