The usual way to pre-populate a form field is to set the value to be a PHP variable.
<input type='text' name='name' id='name' value='<?php echo $value; ?>' />
Where you create the variable is up to you. It can be from a previous showing of the form, or a default value generated in your PHP, etc.
For <select> and radio buttons you can pre-select a default using 'selected' like this:
<select name='status' id='status' >
<option value='prov' selected='selected'>Provisional</option>
(I have read that it's no longer necessary to use "selected='selected'", you can just use "selected", but I've not proved this for myself).
It's not clear to me whether you want to pre-set the selects and radio buttons, or take the user selections and use them to put values into other form fields (such as text inputs or text areas) ? If you can tell me a bit more I'll try to answer more fully.