simple help with a form

Hi i am making my own website. Ive made a form and its fine but this is what id like to do. Have my text box have some text in it before youve touched it such as “your email address here” then when you click it to type the writing dissappears enabling you to type. I can mke the original text but when a user trys to type in it they just add to the end which is annoying. PLease help asap! Thanks all
Matt

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