There are a couple of methods you can use to add images to your post.
This first method describes how to add an image from your computer.
You need to be in advanced mode for this. (Not Quick Reply mode.)
Enter the comment you want to make...
Then click the attachment icon. (It looks like a paperclip)
A small window will pop up.
Click on "choose file".
Once you click on "choose file" another window will open up for you to navigate to where the image is located on your computer.
When you have located the image, clicking on it will automatically enter the file name of the image. Once that happens, click on "open".
You will then need to click the upload button. If you do not see it you may need to scroll to the right of the small window until you do.
Once that is done...
Simply click on the paperclip icon again and select the image you want to insert by clicking on the file name. This will insert the code for the image to your post.
Once you click to submit the post, the image will appear.
If you skip the step of inserting the image (where you want it to show in your post) the uploaded images will show as thumbnails at the bottom of the post.
When inserting multiple images or code to your posts, please make sure to put each image (or code) on a new line.