Hover your mouse over my attachment below. It will show you to the button to press. You can choose to link to a URL from the internet or upload a file from your own computer. See if you can figure it out from there and let us know if you have further questions.
Go to reply ..... go to "go advanced" ...... type in whatever text ....... scroll down below the text box and see "manage attachments"
Click on that and a menu appears ...... click add photos ...... another menu appears ..... click 'basic uploader' ....... click "browse"
This should take you to your files. Select the file where your photos are located. Select the photo. Click "open". There is a + sign if you want to add another (up to 5 in one post)
Click "upload". When it uploads click "insert inline" and then "done"
Alternatively you can upload on a free web site such as Photobucket and copy and paste the URL for your photo in the text box.