After opening your image in photoshop maximise photoshop, hit the Tabs button. This closes all tabs and gives you a better space to see what you doin. Then hit F7 which opens the layers tab. then go to the windows menu flyout near the top of your screen select tools, look for the icon that looks like a pen use this to create an outline around the object,(i usually zoom in by pressing ctrl- + and when i've zoomed in as far as i'd like i press the spacebar to navigate my way around the image. once you happy with the outline go to the paths tab you should find a path thats named workpath press your ctrl key and while holding it down click on workpath. This creates a selection. Go to your layers tab rightclick your background layer and select the duplicate background layer option, hit enter, then with that layer selected hit delete. If the part of your image you want to use deletes then press ctrl-z (the dash means you pressing these buttons simultaneously). Then press ctrl-shift-i then press delete again this should delete the part you don't want save the document as a photoshop image. Then delete your background layer. Go to File>Save As and save your image as a .png or a .gif select the transparency and interlace options.