Custom Nightmare

I’m having a hard time figuring out the most basic of things – so much so that I’m feeling completely stupid here 🙁

I have a few custom fields. A few with text (designed_by, copyright) and one that is a link. I want to be able to show these on each post just under the content.

I have been to the documentation, but I just cannot seem to get these things to work.

Where exactly in the single.php do I put what code?