PHP : Form help

[size=1][color=darkslategray]How do you make a button that you can click to add information to a text field?[/color][/size]
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[size=1][color=darkslategray]eg;[/color][/size]
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[size=1][color=darkslategray]Click the button with a B on it and add “< b >” to the the text field.[/color][/size]
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[size=1][color=darkslategray]eg2;[/color][/size]
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[size=1][color=darkslategray]Click the code button to add " [ CODE ] " to your text field.[/color][/size]
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[size=1][color=#2f4f4f]//KinZo[/color][/size]