Can you access the console? Good. Then let's proceed.
Bring down the console.
Type the command you wish to execute, in this case 'bind <key> <command>.
For instance, 'bind t +taunt;-taunt' as in the message above. Type this without the quotes.
That's it. Now remove the console, and try it by pressing the key you bound, and it'll perform the command you bound to it.