Make sure it shows up. Then tweak it to fit what's on your page.
Watch out - don't delete the closing bracket for the IMG tag or other stuff on your page won't work properly anymore! You can see this has happened if the next tag is red instead of blue.
Just add the bracket back in and everything will be fine.
When you've added all your pictures, clean up your folder and resize any pictures as needed...
Most of your photos will the JPGs. If your photo doesn't show up on the page, check the file type in your folder. The extensions are as follows:
In your webpage folder, change View to "Details"...
Then you'll see if your pictures are not JPGs, what they are in the file type column...
Try to add at least one animated GIF. Save it with "anim" at the end of the name.
Try to find one picture with a transparent background. Save it with "transp" at the end of the name. The file type should be PNG. Any transparent pictures you have should have no border!