When you are ready to upload observations, go to Menu/Observations and click the upload button on the toolbar. You need to have an active network connection for upload to work.
After clicking the upload button, a message is shown with the number of observations and photos that will be uploaded, and a question for confirmation. After confirmation you'll see a progress indicator. During the upload you cannot use iObs. You can cancel the upload any time by tapping on the progress indicator.