Go to the bottom of the text window as shown here and click on the link circled in red-
A small window should open up as shown. Now click on 'browse' circled in red.
This will open up a file window where you browse for your picture files. I usually keep these on my desktop.
Click on the file you want and click 'open' and select the 'family safe' radio button, then click on 'upload it!'.
You should then be returned back to your post, but there will be some text and code in your window, which is the picture you have posted.