So you want to use special characters from any specific font but do not have any idea how to do so? I had a look around and Google but did not find an appropriate answer so I tried myself and here is how I copied the Font Awesome and used it into my favorite Photoshop app.
Step 1: Hit command + space to open the spotlight.
Step 2: Type Font Book and you will see it into results, just select it and open.
Step 3: Select Font Awesome from the list and you will be able to see all special character.
Step 4: Select an icon you want and copy it using command + c. That is it, now you can past icon using Photoshop text tool.
Hope this help.