First, welcome to the site! Lots of friendly folks here who are happy to help...
Can you provide additional info such as the mode you were shooting in (Program, Aperture or Shutter Priority, Manual)? I don't use Picasa, but most photo editors will be able to show you the settings when the image was taken - ISO, Aperture and Shutter speed. All of that info can help us figure out what may have occurred to cause the issue...
That said, there appear to be some areas which are sharp in each image which to me indicates your issue may be the aperture and / or the focus point. For example, the front left of the car is in focus as are the sunglasses on the lady. Those were likely the focus points that the camera chose to focus on when the image was taken. When you focus, the camera generally will light up a square in the viewfinder that tells you where the camera has focused. First suggestion would be to make sure that point is where you want it to focus before taking the photo. You can control the # of focus points in the menu and some situations may be better served by reducing the # of focus points.
There are three settings as mentioned above, ISO, Aperture and Shutter speed that combine to create an image. The ISO controls how sensitive the sensor is to light. The higher the ISO, the less light is required to capture the image, but it will introduce more grain in the image. The shutter speed controls how long the sensor is exposed to light and can be used to both stop or introduce motion in an image - for example, freezing the motion of the waterfall with a fast shutter speed or blurring the movement of the waterfall with a slower shutter speed. The aperture controls the depth of field in the image. The depth of field is the range (front to back) in the image that appears in focus. The wider the aperture (smaller number) the less depth of field will be available in the image. That allows the photographer to get more DOF on photos like landscapes where they may want most of the image in focus and less DOF in something like a portrait where they may only want the subject to be in focus. Your photo of rocks above is a good example of DOF as it shows the range of the image that is in focus fairly clearly with the foreground and background blurred.
These three settings are tied together to create a correctly exposed image. In Program mode, the camera makes all these decisions for the photographer. In Aperture Priority, the photographer sets the desired aperture and allows the camera to make the other decisions. In Shutter Priority, the photographer sets the desired shutter speed and allows the camera to make the other decisions. In Manual, the photographer controls both aperture and shutter. ISO is set in the menu and can be specifically set or Auto-ISO set to allow the camera to change the ISO based on the other settings the photographer uses.
Hope that helps...