These are called Smilies and are to the right of the text box within which you type your message. Smilies are small graphical icons which you can insert into your messages to convey an emotion or feeling, such as a joke or embarrassment. For example, if you entered a sarcastic comment, rather than type 'that was a joke', you could simply insert the 'wink' smilie.
If you have used email or internet chat systems, you will probably be familiar with the concept of smilies already. Certain combinations of text characters are converted into smilies. For example,

is converted into a smiling face. To understand smilie codes, tilt your head to the left and look at the text: you will see that

represents two eyes and a smiling mouth.
On occasions, you may want to prevent the text in your message being converted into smilies. You will see a checkbox which you can select when you make a new post, which will allow you to 'Disable Smilies'.
The Smilies are different from Post Icons. Post Icons put the icon in the thread view where as smilies put this icon in your actual message. For example this thread is marked with a "cool" icon. Post Icons convey emotion for an entire thread where smilies convey an emotion for a particular part of your thread. For instance, this means wink

.