If in a form i set
<input type = 'text' name = 'entry' value ='default_text'/>
And a user enters 'foo' in place of 'default_text' is this enough to make $_POST['entry'] become 'foo' instead of 'default_text'?
If not how do i make that happen?
If someone enters text into this input:
PHP will receive the new text in $_POST/$_GET/$_REQUEST etc. and not the default (so, to answer your question, yes that is enough).