You can use the "upload" link in the upper blue bar. Once uploaded, at the bottom of the upload page is a link "my uploads", click on the link to find your picture; use the IMG link to paste into your post. Be sure the link looks like this
Please notice the space and ~ between the picture and the blocks - they were added by me to show you the link - for the picture to show, yours will have no spaces and no ~.
looks like this : [IMG]https://www.backyardchickens.com/forum/uploads/31162_dsc_0785.jpg
Its really easy: put your pictures on your computer then go to the blue bar above and click on 'Uploads". Click the 'Browse" button and choose your photo (double click it) and then click the 'Submit' button. When it loads, there will be two address lines under the thumbnail of your photo. Highlight the second address line, right click and hit 'copy' then paste to your post. It will copy the 'address' but when you submit your post, it will be the picture that you chose. Hope this makes sense-