Step 1: Paste the command in a command block
Step 2: Make sure your in minecraft 1.9
Step 3: Make the command block "Always Active"
Step 4: Make sure the command block is in "Impulse"
Step 5: Change The "[Your Username]" to your minecraft username e.g "/tellraw PinkSheepYT {"text":"You Rock","color":"red","bold":true,"extra":[{"text":" :)","color":"blue","bold":true}]} to say "You Rock :)" to Pink Sheep"
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I used OptiFine when i did this
Butt, uhh i mean, But you don't need OptiFine