Format a Post
When you create a new thread or a new post in an existing thread (using the New Reply button rather than the Quick Reply), you will see menu options for formatting your post.

The gray bars above the text window give you options.
The second gray bar lets you change the subject.
The third gray bar lets you assign an icon to the post, which is visible in the list of posts.
The fourth gray bar has the text window in it. On the left it has smilies you can select. Above the text bar it has various formatting options, such as italics, bold, underline, and strikethrough. This is also where you can insert links.
To add an image (a picture), you either need to be using the Tapatalk app (which will let you load an image to the forum directly) or load your picture to some other webhost (like Dropbox or Google) that let's you share images with other sites. Then you can use the Insert an Image button to post your link to the externally hosted image, which will be inserted in your post.