The icons are just emojis built into the forum code
You can access those with : and then typing something out like :fire 
The outlined boxes are a quote-tag with the ‘author’ portion removed.
using a
>will start the box without needing something to highlight/quote something to make the box.
<> and </> tags can be used to increase or decrease the size of the text with big/small tags respectively. Text in <> also gets hidden so posters can bypass the character limited by <typing whatever between the arrows>
Sami has a pinned topic on how to do spiffy stuff like that on the forums here