For the smaller faces such as these
You have to go to the right of send when sending a message and click emoticons and there will be a whole tab of them, and just copy the link on the left.
For faces such as these
These are plz accounts that people have made to be placed into messages. To do this you have to put (without the spaces)
:icon (whatever the account name is):
For faces, they usually have a plz on the end of the name to tell them apart from real accounts, and there is no useful database on the side so you will either have to post the code for them on word or something, or just remember them. There is probably thousands though, so I bet if you just type in something and put plz on the end you may have something (try preview before sending though XD)
You can do this with actual accounts as well. For example