Step 1: Connect the Camera to Your Computer
Connect the cable to the camera and then to the computer.
Step 2: Launch Image Capture
Find Image Capture in your Applications folder, and double-click it to launch it.
You will see a window, with a "Devices" tab in the left column. Under that tab should be an icon representing your camera. And in the main body of the window, you should see thumbnails of all of the images stored on your camera.
If not, be sure the cable is securely connected to both the camera and the computer. You could try unplugging and plugging it in again. You can also try quitting and relaunching the Image Capture application.
If it just won't show up, your camera may not be compatible with the Macintosh, and you will have to find another way to get your pictures from your camera into your Mac.
Step 3: Select the Images and Import Them
Select the thumbnails of the images you want on your computer then click the "Import" button in the bottom right corner of the window. OR, you can click "Import All" to get all of the pictures on the camera.
Step 4: Open the Image File You Want to Work On
You can now open up the image program you are working with, like Photoshop, GIMP, or something else, and select "Open" from the "File" menu. You'll see a file dialog box. Use that to navigate to the folder where you imported your images, find the image you want to work on, and double click it.
Or, you can use the Finder and open the folder where you imported the image, and hold down the control key while you click down on the file icon. A menu is displayed. Scroll down to select "Open With", and then you'll see another menu that lists all of the applications on your computer that can open the image file. Try some of them out, see what happens! You can always quit if things get strange!