Download a free graphics program such as GIMP or Pixia if you don't already have one you can use. Alternatively, you can use a free online image editor that has many of the same functions and tools as other image editors.
Save any images you would like to include in your banner image to your desktop or a folder. Having all of your images in one place makes it easy to access them all at once.
Open your graphics program or open the online image editor you want to use. Click "File" then click "Open" and open the images you want to use. To select multiple images at once, click one, hold down the "Shift" key and click other images. If this doesn't work, you may need to open them one at a time.
Create a new image by clicking "File" then "New." Enter the size of your image (this file will be your banner) and click "OK." This step may vary according to your program of choice. The file will be blank, but you can add to it later.
Select an image that you want to use in the banner, then select the rectangular selection tool. This tool is typically in your program's tool bar and looks like a box with dotted lines. Use this tool to select whatever part of the image you want to use. Once you have made your selection, click "Edit," then "Copy." Select your blank banner document, then click "Edit" then "Paste." The image will appear on your banner and you can position it wherever you like.
Experiment with the other tools, such as the brush and text tools to add effects and words to your banner. If you make a mistake, look in the "History" box somewhere on the screen. This displays every step that was taken, so you can click on one of your previous steps to undo anything that was done to the image.
When you are finished, click "File" then "Save." Save the image to your desktop, then upload it to your website's file manager or a free online image host such as wimg.co.uk or tinypic.com.