In the "Reply" box click "Go Advanced" at the bottom right. You can add your initial text, and then with your cursor at the place where you want your first picture scroll down to Additional Options and click the box "Manage Attachments" which opens a smaller box, "File Upload Manager". In that box click "Add Files" and choose the picture file from your computer (may have to be reduced in size, nominal 650-750KB) and click "Open", and then "Upload". Your file will be in a box at the bottom, checkmarked for uploading. To the right click "Insert Inline", and then "Done". Your picture file will be in your text entry, and you can hit "Preview Post" to confirm.

You can add up to 5 pictures to a thread in this manner, repeating the steps with text added between the pictures, or by uploading five at once. The files can be moved around by highlighting and dragging them or by cut & paste. Sounds a lot more complicated than it is, once you do one you'll be an expert.