At the very top you have your title bar telling you that it is the New Image dialog box. Just below that you have an area for preset sizes. Click the arrow to expand the list of pre-made files. We will cover them more in depth at a later time, but I wanted to make you aware that they are there.
Go to the Image Dimensions area and under Units you have several options to choose from such as pixels, inches, centimeters, and millimeters. Most people work with the pixel option unless they are doing a lot of printing. For these exercises, please make sure this is set to PIXELS and then the one directly below it to PIXELS PER INCH. For Width, enter 375 and do the same for the Height. Leave the resolution set to 200 for now.
Under Image Characteristics, there are three options for the type of background; Raster, Vector and Art Media. Raster is the one you will use the most, so choose that now. Set the color depth to RGB 8-bit. If your background color is not set to white already, simply click the box and the color picker dialog will display for you to choose a white color. We will cover that more in depth at a later time as well.
After you have made your adjustments to match mine shown here then click OK. The dialog box will close and new blank image with a white background will be open in your workspace.