Usually just pressing the Image icon, pasting the URL to the image with the .jpg / .png at the end, then it will appear in the post with [img] and [/img] either end.
You could also use IMGbb >
https://imgbb.com to upload your pictures. Upload an image, choose "do not delete" then under Embed codes, choose BBCode Full and just copy the whole link and paste into your post.
Be sure to keep the images around 1024px wide, other wise they become huge on the forum.
