I uses Picasa most of the time to enhance my photographs. I find it more simple and useful if compared to a much complicated Adobe Photoshop. Here some steps on how to use this tool.

Step 1: Double click to open the picture you would like to enhance

Step 2: Now you are in the editing view

Step 3: Click the Tuning tab, adjust Highlights to increase the brightness and adjust the Shadows to increase the contrast of the photo. This photo color too warm, I have adjusted the Color Temperature to left to reduce the warmness.

Step 4: Now click on Effects tab for more enhancement. I have selected Saturation and to give the photo a little bit more vivid.

Step 5: Next, I click Glow to give the photo some gauzy glow feel.

Step 6: I would like to make the blue sky darker to simulate polarizer effect. I have used Graduated Tint and adjust the Feather value to maximum to give the smoothest feel and increase the Shade value to darken the sky.

Now I am done and satisfied with the result and I am ready to export this enhanced photo to a smaller size.

Step 7: Click File -> Export Picture to Folder…

Step 8: In this window, you can select the size and image quality that you want to export. For this photo, I have selected 1024 x 768 and Maximum Image Quality.

Step 9: Compare the exported and edited copy against the original image. Now you should be able to see that the image has become much better.