If you use the Go Advanced controls then you'll find a paper clip icon in the toolbar when you're composing your post. Click that and it opens the Attachment Manager window. You can upload your images there.

When you want to place the images in your post, click the arrow beside the paperclip and you'll see a list of your attachments. You can select each one and place them in the text as you're composing your post. You can attach a maximum of 5 images to a given post.