Syntax question:

I am able to insert new data via a php script using this code:
values ('', '', 'this is the title', 'this is the body')

Now, how do I pass through variables that have been collected from a form. I tried this and got errors:
values ('', '', '$_POST["title"]', '$_POST["body"]')
I also tried it without the single quotes around the variables, but got errors.

I know this must seem funny, but I just don't know how to write this correctly yet.