When you write or reply to posts you'll see the box you can type inside. Scroll down the page and you'll see lots of stuff under the heading "Additional options".
Click the "manage attachments" button and a pop up will appear. If the photos are on your computer then click the "browse" button at the top, and it will open up windows explorer. Select the file you want to post, then click open. Then click on "uplolad" and the photo should be loaded into your post.