How to insert a piece of php code into a page

[inteltone]

Hi!
Please, tell me how to insert a piece of php code into a page.

I have read in wiki about Guestbook plugin. There is a line there
"The guestbook must be called so in a template (or a page with exec plugin)..."

What is the exec plugin?

I'm new to GetSimple but am very interested in learning it as quickly as possible. It's a really great CMS.

Thanks in advance