php project

Hi Any body know about placeholders? I have a website where i need placeholders. Placeholder => [username] Placeholder => [email].... If user will write [username] on his page then page will get his username from address bar to add it in MYSQL quesry so quesry will get all data of this username and user can get his info using [username], [email], [phone]...... Let me know if anyone can do this Advance Thanks Sarm