When creating/editing a post, you click the fourth icon from the left, above your text box. It should look like a picture frame. A pop up box should appear and you follow the instructions, entering the URL/link to an image from another site.
If you want to use an image from your own computer, you can upload images to image sharing websites such as "Imgur" and then link to the picture you uploaded from there.
Comments
When creating/editing a post, you click the fourth icon from the left, above your text box. It should look like a picture frame. A pop up box should appear and you follow the instructions, entering the URL/link to an image from another site.
If you want to use an image from your own computer, you can upload images to image sharing websites such as "Imgur" and then link to the picture you uploaded from there.