There are several ways to add a photo to a page. This one should get you started:

You'll need the photo saved on your computer as either gif, jpg or png (doesn't really matter which, but if you have the choice jpg or jpeg is usually best).

Open your page to edit it. Click at the point where you want the photo to be and then click the insert/edit image button (it looks like a photo of a tree - it's about two-thirds the way along the bottom row of editor buttons). 

A box will appear on screen. 

Click on the icon at the right-hand side of where it says image URL (it's quite small so easy to overlook if you're not aware of it - it looks like a square with 6 red dots). 

This will open another box allowing you to choose the photo that you want to add. You'll see there are two sections: select an existing image and add a new image.

For now, look under add a new image and type a name for your photo in the file name box. For your own sanity, use something meaningful or descriptive for the name (not something like 'photo 1' or 'IMG2371.JPG') - the photo will be stored in your site's asset library using this name, so a good name will be really helpful if you need to find it again at a later date!)

Click the choose file button (next to where it says upload image). This will allow you to select the photo on your computer.

Lastly, click the save and publish button. This may take a few seconds, but when it is done you'll be back at the first box and you'll see a preview of your photo.

Type a quick description of your photo into the box labelled image description and then click insert. The photo will be added to your page.

The photo will also be added to your site's asset library so, should you need it again for another page, you can choose it from the select an existing image list mentioned above (which is why giving it a good name is important).

Hope this helps, but reply here if it doesn't.